report correct content size in AtomNSWindow

The views framework relies on NSWindow to return content size of window,
since we don't use the borderless window, the original result would
include titlebar. We have to override the function to return correct
result for frameless window.

atom/browser/ui/cocoa/atom_ns_window.mm

@@ -7,6 +7,7 @@
 #include "atom/browser/native_window_mac.h"
 #include "atom/browser/ui/cocoa/atom_preview_item.h"
 #include "atom/browser/ui/cocoa/atom_touch_bar.h"
+#include "ui/base/cocoa/window_size_constants.h"
 
 namespace atom {
 
@@ -23,14 +24,25 @@ bool ScopedDisableResize::disable_resize_ = false;
 @synthesize windowButtonsOffset;
 @synthesize vibrantView;
 
-- (void)setShell:(atom::NativeWindowMac*)shell {
-  shell_ = shell;
+- (id)initWithShell:(atom::NativeWindowMac*)shell
+          styleMask:(NSUInteger)styleMask {
+  if ((self = [super initWithContentRect:ui::kWindowSizeDeterminedLater
+                               styleMask:styleMask
+                                 backing:NSBackingStoreBuffered
+                                   defer:YES])) {
+    shell_ = shell;
+  }
+  return self;
 }
 
 - (atom::NativeWindowMac*)shell {
   return shell_;
 }
 
+- (NSRect)originalContentRectForFrameRect:(NSRect)frameRect {
+  return [super contentRectForFrameRect:frameRect];
+}
+
 - (NSTouchBar*)makeTouchBar API_AVAILABLE(macosx(10.12.2)) {
   if (shell_->touch_bar())
     return [shell_->touch_bar() makeTouchBar];
@@ -52,6 +64,13 @@ bool ScopedDisableResize::disable_resize_ = false;
   }
 }
 
+- (NSRect)contentRectForFrameRect:(NSRect)frameRect {
+  if (shell_->has_frame())
+    return [super contentRectForFrameRect:frameRect];
+  else
+    return frameRect;
+}
+
 - (NSRect)constrainFrameRect:(NSRect)frameRect toScreen:(NSScreen*)screen {
   // Resizing is disabled.
   if (atom::ScopedDisableResize::IsResizeDisabled())