[mac] Dynamically enable accessibility based on VoiceOver status

atom/browser/mac/atom_application.mm

@@ -8,6 +8,8 @@
 #include "base/strings/sys_string_conversions.h"
 #include "atom/browser/browser.h"
 
+#include "content/public/browser/browser_accessibility_state.h"
+
 @implementation AtomApplication
 
 + (AtomApplication*)sharedApplication {
@@ -46,4 +48,23 @@
   atom::Browser::Get()->OpenURL(base::SysNSStringToUTF8(url));
 }
 
+- (void)accessibilitySetValue:(id)value forAttribute:(NSString *)attribute {
+  // undocumented attribute that VoiceOver happens to set while running.
+  // Chromium uses this too, even though it's not exactly right.
+  if ([attribute isEqualToString:@"AXEnhancedUserInterface"]) {
+    [self updateAccessibilityEnabled:[value boolValue]];
+  }
+  return [super accessibilitySetValue:value forAttribute:attribute];
+}
+
+- (void)updateAccessibilityEnabled:(BOOL)enabled {
+  content::BrowserAccessibilityState *ax_state = content::BrowserAccessibilityState::GetInstance();
+
+  if (enabled) {
+    ax_state->OnScreenReaderDetected();
+  } else {
+    ax_state->DisableAccessibility();
+  }
+}
+
 @end