[content] Fix background color update handling in RWHVAura.

content/browser/frame_host/render_widget_host_view_child_frame.h

Index: content/browser/frame_host/render_widget_host_view_child_frame.h
diff --git a/content/browser/frame_host/render_widget_host_view_child_frame.h b/content/browser/frame_host/render_widget_host_view_child_frame.h
index c0eb3fa328bc74aa1772b54ec8f198cf2ab2bd94..ea42f24d6df5aca81d559fd2144966f5d3a28420 100644
--- a/content/browser/frame_host/render_widget_host_view_child_frame.h
+++ b/content/browser/frame_host/render_widget_host_view_child_frame.h
@@ -89,6 +89,7 @@ class CONTENT_EXPORT RenderWidgetHostViewChildFrame
   gfx::NativeView GetNativeView() const override;
   gfx::NativeViewAccessible GetNativeViewAccessible() override;
   void SetBackgroundColor(SkColor color) override;
+  SkColor background_color() const override;
   gfx::Size GetPhysicalBackingSize() const override;
   bool IsMouseLocked() override;
   void SetNeedsBeginFrames(bool needs_begin_frames) override;
@@ -255,6 +256,9 @@ class CONTENT_EXPORT RenderWidgetHostViewChildFrame
 
   bool has_frame_ = false;
 
+  // The background color of the widget.
+  SkColor background_color_;
+
   base::WeakPtrFactory<RenderWidgetHostViewChildFrame> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewChildFrame);
 };