[Mac] Use a custom view to implement colored app windows.

chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h

Index: chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
diff --git a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
index b8aef3d69fc3a8307df9290958c192582491edee..da61ae216099063531bb1ddbd201662c47e7ed97 100644
--- a/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
+++ b/chrome/browser/ui/cocoa/apps/native_app_window_cocoa.h
@@ -43,6 +43,16 @@ class SkRegion;
 
 @end
 
+// A view that paints a solid color. Used to change the title bar background.
+@interface TitlebarBackgroundView : NSView {
+ @private
+  base::scoped_nsobject<NSColor> color_;
+  base::scoped_nsobject<NSColor> inactiveColor_;
+}
+- (void)setColor:(NSColor*)color
+   inactiveColor:(NSColor*)inactiveColor;
+@end
+
 // Cocoa bridge to AppWindow.
 class NativeAppWindowCocoa : public extensions::NativeAppWindow,
                              public content::WebContentsObserver {
@@ -206,6 +216,7 @@ class NativeAppWindowCocoa : public extensions::NativeAppWindow,
   SkColor inactive_frame_color_;
 
   base::scoped_nsobject<NativeAppWindowController> window_controller_;
+  base::scoped_nsobject<TitlebarBackgroundView> titlebar_background_view_;
 
   // For system drag, the whole window is draggable and the non-draggable areas
   // have to been explicitly excluded.