diff --git a/content/browser/accessibility/browser_accessibility_cocoa.h b/content/browser/accessibility/browser_accessibility_cocoa.h
index a03585269db6..e7b028760bba 100644
--- a/content/browser/accessibility/browser_accessibility_cocoa.h
+++ b/content/browser/accessibility/browser_accessibility_cocoa.h
@@ -111,7 +111,9 @@ struct AXTextEdit {
 @property(nonatomic, readonly) NSNumber* enabled;
 // Returns a text marker that points to the last character in the document that
 // can be selected with Voiceover.
+#ifndef MAS_BUILD
 @property(nonatomic, readonly) id endTextMarker;
+#endif
 @property(nonatomic, readonly) NSNumber* expanded;
 @property(nonatomic, readonly) NSNumber* focused;
 @property(nonatomic, readonly) NSNumber* grabbed;
@@ -147,12 +149,16 @@ struct AXTextEdit {
 @property(nonatomic, readonly) NSArray* selectedChildren;
 @property(nonatomic, readonly) NSString* selectedText;
 @property(nonatomic, readonly) NSValue* selectedTextRange;
+#ifndef MAS_BUILD
 @property(nonatomic, readonly) id selectedTextMarkerRange;
+#endif
 @property(nonatomic, readonly) NSValue* size;
 @property(nonatomic, readonly) NSString* sortDirection;
 // Returns a text marker that points to the first character in the document that
 // can be selected with Voiceover.
+#ifndef MAS_BUILD
 @property(nonatomic, readonly) id startTextMarker;
+#endif
 // A string indicating the subrole of this object as far as accessibility
 // is concerned.
 @property(nonatomic, readonly) NSString* subrole;
diff --git a/content/browser/accessibility/browser_accessibility_cocoa.mm b/content/browser/accessibility/browser_accessibility_cocoa.mm
index bc4b972f9c78..fb06c95af750 100644
--- a/content/browser/accessibility/browser_accessibility_cocoa.mm
+++ b/content/browser/accessibility/browser_accessibility_cocoa.mm
@@ -122,6 +122,7 @@ NSDictionary* attributeToMethodNameMap = nil;
 // VoiceOver uses -1 to mean "no limit" for AXResultsLimit.
 const int kAXResultsLimitNoLimit = -1;
 
+#ifndef MAS_BUILD
 extern "C" {
 
 // The following are private accessibility APIs required for cursor navigation
@@ -328,6 +329,7 @@ NSAttributedString* GetAttributedTextForTextMarkerRange(
   AddMisspelledTextAttributes(text_only_objects, attributed_text);
   return [attributed_text attributedSubstringFromRange:range];
 }
+#endif
 
 // Returns an autoreleased copy of the AXNodeData's attribute.
 NSString* NSStringForStringAttribute(
@@ -581,7 +583,9 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
       {NSAccessibilityDOMIdentifierAttribute, @"domIdentifier"},
       {NSAccessibilityEditableAncestorAttribute, @"editableAncestor"},
       {NSAccessibilityEnabledAttribute, @"enabled"},
+#ifndef MAS_BUILD
       {NSAccessibilityEndTextMarkerAttribute, @"endTextMarker"},
+#endif
       {NSAccessibilityExpandedAttribute, @"expanded"},
       {NSAccessibilityFocusedAttribute, @"focused"},
       {NSAccessibilityGrabbedAttribute, @"grabbed"},
@@ -614,13 +618,17 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
       {NSAccessibilityRowsAttribute, @"rows"},
       // TODO(aboxhall): expose
       // NSAccessibilityServesAsTitleForUIElementsAttribute
+#ifndef MAS_BUILD
       {NSAccessibilityStartTextMarkerAttribute, @"startTextMarker"},
+#endif
       {NSAccessibilitySelectedAttribute, @"selected"},
       {NSAccessibilitySelectedChildrenAttribute, @"selectedChildren"},
       {NSAccessibilitySelectedTextAttribute, @"selectedText"},
       {NSAccessibilitySelectedTextRangeAttribute, @"selectedTextRange"},
+#ifndef MAS_BUILD
       {NSAccessibilitySelectedTextMarkerRangeAttribute,
        @"selectedTextMarkerRange"},
+#endif
       {NSAccessibilitySizeAttribute, @"size"},
       {NSAccessibilitySortDirectionAttribute, @"sortDirection"},
       {NSAccessibilitySubroleAttribute, @"subrole"},
@@ -1091,6 +1099,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
                      ax::mojom::Restriction::kDisabled];
 }
 
+#ifndef MAS_BUILD
 // Returns a text marker that points to the last character in the document that
 // can be selected with VoiceOver.
 - (id)endTextMarker {
@@ -1102,6 +1111,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   BrowserAccessibilityPositionInstance position = root->CreatePositionAt(0);
   return CreateTextMarker(position->CreatePositionAtEndOfAnchor());
 }
+#endif
 
 - (NSNumber*)expanded {
   if (![self instanceActive])
@@ -1975,6 +1985,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   return [NSValue valueWithRange:NSMakeRange(selStart, selLength)];
 }
 
+#ifndef MAS_BUILD
 - (id)selectedTextMarkerRange {
   if (![self instanceActive])
     return nil;
@@ -2007,6 +2018,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
                                                anchorAffinity, *focusObject,
                                                focusOffset, focusAffinity));
 }
+#endif
 
 - (NSValue*)size {
   if (![self instanceActive])
@@ -2039,6 +2051,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   return nil;
 }
 
+#ifndef MAS_BUILD
 // Returns a text marker that points to the first character in the document that
 // can be selected with VoiceOver.
 - (id)startTextMarker {
@@ -2050,6 +2063,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   BrowserAccessibilityPositionInstance position = root->CreatePositionAt(0);
   return CreateTextMarker(position->CreatePositionAtStartOfAnchor());
 }
+#endif
 
 // Returns a subrole based upon the role.
 - (NSString*) subrole {
@@ -2335,12 +2349,14 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
   NSMutableAttributedString* attributedValue =
       [[[NSMutableAttributedString alloc] initWithString:value] autorelease];
 
+#ifndef MAS_BUILD
   if (!browserAccessibility_->IsTextOnlyObject()) {
     std::vector<const BrowserAccessibility*> textOnlyObjects =
         BrowserAccessibilityManager::FindTextOnlyObjectsInRange(
             *browserAccessibility_, *browserAccessibility_);
     AddMisspelledTextAttributes(textOnlyObjects, attributedValue);
   }
+#endif
 
   return [attributedValue attributedSubstringFromRange:range];
 }
@@ -2460,6 +2476,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
     return nil;
   }
 
+#ifndef MAS_BUILD
   if ([attribute isEqualToString:@"AXUIElementForTextMarker"]) {
     BrowserAccessibilityPositionInstance position =
         CreatePositionFromTextMarker(parameter);
@@ -2637,6 +2654,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
     NSString* text = GetTextForTextMarkerRange(parameter);
     return [NSNumber numberWithInt:[text length]];
   }
+#endif
 
   if ([attribute isEqualToString:
       NSAccessibilityBoundsForRangeParameterizedAttribute]) {
@@ -2674,6 +2692,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
     return nil;
   }
 
+#ifndef MAS_BUILD
   if ([attribute isEqualToString:
            NSAccessibilityLineTextMarkerRangeForTextMarkerParameterizedAttribute]) {
     BrowserAccessibilityPositionInstance position =
@@ -2753,6 +2772,7 @@ NSString* const NSAccessibilityRequiredAttributeChrome = @"AXRequired";
 
     return @(child->GetIndexInParent());
   }
+#endif
 
   return nil;
 }
diff --git a/content/browser/accessibility/browser_accessibility_manager_mac.mm b/content/browser/accessibility/browser_accessibility_manager_mac.mm
index 134f855de654..d588ed98839d 100644
--- a/content/browser/accessibility/browser_accessibility_manager_mac.mm
+++ b/content/browser/accessibility/browser_accessibility_manager_mac.mm
@@ -441,6 +441,7 @@ NSDictionary* BrowserAccessibilityManagerMac::
       [user_info setObject:native_focus_object
                     forKey:NSAccessibilityTextChangeElement];
 
+#ifndef MAS_BUILD
       id selected_text = [native_focus_object selectedTextMarkerRange];
       if (selected_text) {
         NSString* const NSAccessibilitySelectedTextMarkerRangeAttribute =
@@ -448,6 +449,7 @@ NSDictionary* BrowserAccessibilityManagerMac::
         [user_info setObject:selected_text
                       forKey:NSAccessibilitySelectedTextMarkerRangeAttribute];
       }
+#endif
     }
   }
 
diff --git a/content/renderer/renderer_main_platform_delegate_mac.mm b/content/renderer/renderer_main_platform_delegate_mac.mm
index 1e2cc38d3868..daa934c345e2 100644
--- a/content/renderer/renderer_main_platform_delegate_mac.mm
+++ b/content/renderer/renderer_main_platform_delegate_mac.mm
@@ -22,6 +22,7 @@
 #include "sandbox/mac/seatbelt.h"
 #include "services/service_manager/sandbox/mac/sandbox_mac.h"
 
+#ifndef MAS_BUILD
 extern "C" {
 void CGSSetDenyWindowServerConnections(bool);
 void CGSShutdownServerConnections();
@@ -30,6 +31,7 @@ void _LSSetApplicationLaunchServicesServerConnectionStatus(
     uint64_t flags,
     bool (^connection_allowed)(CFDictionaryRef));
 };
+#endif
 
 namespace content {
 
@@ -38,6 +40,7 @@ namespace {
 // This disconnects from the window server, and then indicates that Chrome
 // should continue execution without access to launchservicesd.
 void DisconnectWindowServer() {
+#ifndef MAS_BUILD
   // Now disconnect from WindowServer, after all objects have been warmed up.
   // Shutting down the connection requires connecting to WindowServer,
   // so do this before actually engaging the sandbox. This may cause two log
@@ -54,6 +57,7 @@ void DisconnectWindowServer() {
       0, ^bool(CFDictionaryRef options) {
         return false;
       });
+#endif
 }
 
 // You are about to read a pretty disgusting hack. In a static initializer,
diff --git a/device/bluetooth/bluetooth_adapter_mac.mm b/device/bluetooth/bluetooth_adapter_mac.mm
index bb996bfd0876..eea959855615 100644
--- a/device/bluetooth/bluetooth_adapter_mac.mm
+++ b/device/bluetooth/bluetooth_adapter_mac.mm
@@ -32,6 +32,7 @@
 #include "device/bluetooth/bluetooth_low_energy_central_manager_delegate.h"
 #include "device/bluetooth/bluetooth_socket_mac.h"
 
+#ifndef MAS_BUILD
 extern "C" {
 // Undocumented IOBluetooth Preference API [1]. Used by `blueutil` [2] and
 // `Karabiner` [3] to programmatically control the Bluetooth state. Calling the
@@ -45,6 +46,7 @@ extern "C" {
 // [4] https://support.apple.com/kb/PH25091
 void IOBluetoothPreferenceSetControllerPowerState(int state);
 }
+#endif
 
 namespace {
 
@@ -118,8 +120,10 @@ BluetoothAdapterMac::BluetoothAdapterMac()
       controller_state_function_(
           base::BindRepeating(&BluetoothAdapterMac::GetHostControllerState,
                               base::Unretained(this))),
+#ifndef MAS_BUILD
       power_state_function_(
           base::BindRepeating(IOBluetoothPreferenceSetControllerPowerState)),
+#endif
       should_update_name_(true),
       classic_discovery_manager_(
           BluetoothDiscoveryManagerMac::CreateClassic(this)),
@@ -302,8 +306,12 @@ bool BluetoothAdapterMac::IsLowEnergyAvailable() {
 }
 
 bool BluetoothAdapterMac::SetPoweredImpl(bool powered) {
+#ifndef MAS_BUILD
   power_state_function_.Run(base::strict_cast<int>(powered));
   return true;
+#else
+  return false;
+#endif
 }
 
 void BluetoothAdapterMac::RemovePairingDelegateInternal(
diff --git a/media/audio/BUILD.gn b/media/audio/BUILD.gn
index 8754161b0c90..7705c0dcc5cf 100644
--- a/media/audio/BUILD.gn
+++ b/media/audio/BUILD.gn
@@ -194,6 +194,12 @@ source_set("audio") {
       "mac/scoped_audio_unit.cc",
       "mac/scoped_audio_unit.h",
     ]
+    if (is_mas_build) {
+      sources -= [
+        "mac/coreaudio_dispatch_override.cc",
+        "mac/coreaudio_dispatch_override.h",
+      ]
+    }
     libs += [
       "AudioToolbox.framework",
       "AudioUnit.framework",
diff --git a/media/audio/mac/audio_manager_mac.cc b/media/audio/mac/audio_manager_mac.cc
index 66a5622f2d3d..b7adea918559 100644
--- a/media/audio/mac/audio_manager_mac.cc
+++ b/media/audio/mac/audio_manager_mac.cc
@@ -864,7 +864,7 @@ AudioParameters AudioManagerMac::GetPreferredOutputStreamParameters(
 
 void AudioManagerMac::InitializeOnAudioThread() {
   DCHECK(GetTaskRunner()->BelongsToCurrentThread());
-  InitializeCoreAudioDispatchOverride();
+  // InitializeCoreAudioDispatchOverride();
   power_observer_.reset(new AudioPowerObserver());
 }
 
diff --git a/net/dns/dns_config_service_posix.cc b/net/dns/dns_config_service_posix.cc
index 06e9d7969c0f..6fc766e981fd 100644
--- a/net/dns/dns_config_service_posix.cc
+++ b/net/dns/dns_config_service_posix.cc
@@ -242,6 +242,7 @@ class DnsConfigServicePosix::Watcher {
 
   bool Watch() {
     bool success = true;
+#ifndef MAS_BUILD
     if (!config_watcher_.Watch(base::Bind(&Watcher::OnConfigChanged,
                                           base::Unretained(this)))) {
       LOG(ERROR) << "DNS config watch failed to start.";
@@ -263,6 +264,7 @@ class DnsConfigServicePosix::Watcher {
                                 DNS_CONFIG_WATCH_MAX);
     }
 #endif  // !defined(OS_ANDROID) && !defined(OS_IOS)
+#endif
     return success;
   }
 
diff --git a/sandbox/mac/sandbox_compiler.cc b/sandbox/mac/sandbox_compiler.cc
index e524aa7b8510..718d3f963da5 100644
--- a/sandbox/mac/sandbox_compiler.cc
+++ b/sandbox/mac/sandbox_compiler.cc
@@ -28,6 +28,7 @@ bool SandboxCompiler::InsertStringParam(const std::string& key,
 }
 
 bool SandboxCompiler::CompileAndApplyProfile(std::string* error) {
+#ifndef MAS_BUILD
   char* error_internal = nullptr;
   std::vector<const char*> params;
 
@@ -44,6 +45,7 @@ bool SandboxCompiler::CompileAndApplyProfile(std::string* error) {
     sandbox::Seatbelt::FreeError(error_internal);
     return false;
   }
+#endif
   return true;
 }
 
diff --git a/sandbox/mac/seatbelt.cc b/sandbox/mac/seatbelt.cc
index dfba0bded9e3..876f96999f53 100644
--- a/sandbox/mac/seatbelt.cc
+++ b/sandbox/mac/seatbelt.cc
@@ -64,7 +64,11 @@ void Seatbelt::FreeError(char* errorbuf) {
 
 // static
 bool Seatbelt::IsSandboxed() {
+#ifndef MAS_BUILD
   return ::sandbox_check(getpid(), NULL, 0);
+#else
+  return true;
+#endif
 }
 
 }  // namespace sandbox
diff --git a/sandbox/mac/seatbelt_extension.cc b/sandbox/mac/seatbelt_extension.cc
index 9073364142e8..2356add74dfa 100644
--- a/sandbox/mac/seatbelt_extension.cc
+++ b/sandbox/mac/seatbelt_extension.cc
@@ -8,6 +8,7 @@
 #include "base/memory/ptr_util.h"
 #include "sandbox/mac/seatbelt_extension_token.h"
 
+#ifndef MAS_BUILD
 // libsandbox private API.
 extern "C" {
 extern const char* APP_SANDBOX_READ;
@@ -18,6 +19,7 @@ char* sandbox_extension_issue_file(const char* type,
                                    const char* path,
                                    uint32_t flags);
 }
+#endif
 
 namespace sandbox {
 
@@ -46,7 +48,11 @@ std::unique_ptr<SeatbeltExtension> SeatbeltExtension::FromToken(
 
 bool SeatbeltExtension::Consume() {
   DCHECK(!token_.empty());
+#ifndef MAS_BUILD
   handle_ = sandbox_extension_consume(token_.c_str());
+#else
+  handle_ = -1;
+#endif
   return handle_ > 0;
 }
 
@@ -58,7 +64,11 @@ bool SeatbeltExtension::ConsumePermanently() {
 }
 
 bool SeatbeltExtension::Revoke() {
+#ifndef MAS_BUILD
   int rv = sandbox_extension_release(handle_);
+#else
+  int rv = -1;
+#endif
   handle_ = 0;
   token_.clear();
   return rv == 0;
@@ -76,9 +86,11 @@ SeatbeltExtension::SeatbeltExtension(const std::string& token)
 char* SeatbeltExtension::IssueToken(SeatbeltExtension::Type type,
                                     const std::string& resource) {
   switch (type) {
+#ifndef MAS_BUILD
     case FILE_READ:
       return sandbox_extension_issue_file(APP_SANDBOX_READ, resource.c_str(),
                                           0);
+#endif
     default:
       NOTREACHED();
       return nullptr;
diff --git a/ui/views/cocoa/bridged_native_widget.mm b/ui/views/cocoa/bridged_native_widget.mm
index c37fd6286340..104cc98f731a 100644
--- a/ui/views/cocoa/bridged_native_widget.mm
+++ b/ui/views/cocoa/bridged_native_widget.mm
@@ -42,6 +42,7 @@
 #include "ui/views/widget/widget_delegate.h"
 #include "ui/views/window/dialog_delegate.h"
 
+#ifndef MAS_BUILD
 extern "C" {
 
 typedef int32_t CGSConnection;
@@ -51,6 +52,7 @@ CGError CGSSetWindowBackgroundBlurRadius(CGSConnection connection,
                                          int radius);
 
 }
+#endif
 
 // The NSView that hosts the composited CALayer drawing the UI. It fills the
 // window but is not hittable so that accessibility hit tests always go to the