[content] Fix background color update handling in RWHVAura.

content/browser/renderer_host/render_widget_host_view_mac.h

Index: content/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.h b/content/browser/renderer_host/render_widget_host_view_mac.h
index 97e927fd734c8519c8f17f52bea8eb1e02b53484..d72039dccd7adef47a5c6a2fb5bf2be5a4a44d77 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.h
+++ b/content/browser/renderer_host/render_widget_host_view_mac.h
@@ -277,6 +277,7 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   bool IsSpeaking() const override;
   void StopSpeaking() override;
   void SetBackgroundColor(SkColor color) override;
+  SkColor background_color() const override;
   void SetNeedsBeginFrames(bool needs_begin_frames) override;
 
   // Implementation of RenderWidgetHostViewBase.
@@ -405,6 +406,10 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
 
   WebContents* GetWebContents();
 
+  // Applies background color without notifying the RenderWidget about
+  // opaqueness changes.
+  void UpdateBackgroundColorFromRenderer(SkColor color);
+
   // These member variables should be private, but the associated ObjC class
   // needs access to them and can't be made a friend.
 
@@ -552,6 +557,9 @@ class CONTENT_EXPORT RenderWidgetHostViewMac
   // Whether a request to flush input has been issued.
   bool needs_flush_input_;
 
+  // The background color of the web content.
+  SkColor background_color_;
+
   // Factory used to safely scope delayed calls to ShutdownHost().
   base::WeakPtrFactory<RenderWidgetHostViewMac> weak_factory_;