Allow to have a transparent UA dependent background.

content/browser/renderer_host/render_widget_host_view_aura.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_AURA_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_AURA_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 108 matching lines @@
   gfx::NativeViewId GetNativeViewId() const override;
   gfx::NativeViewAccessible GetNativeViewAccessible() override;
   ui::TextInputClient* GetTextInputClient() override;
   bool HasFocus() const override;
   bool IsSurfaceAvailableForCopy() const override;
   void Show() override;
   void Hide() override;
   bool IsShowing() override;
   gfx::Rect GetViewBounds() const override;
   void SetBackgroundColor(SkColor color) override;
+  void SetBackgroundOpaque(bool opaque) override;
   gfx::Size GetVisibleViewportSize() const override;
   void SetInsets(const gfx::Insets& insets) override;
 
   // Overridden from RenderWidgetHostViewBase:
   void InitAsPopup(RenderWidgetHostView* parent_host_view,
                    const gfx::Rect& pos) override;
   void InitAsFullscreen(RenderWidgetHostView* reference_host_view) override;
   void MovePluginWindows(const std::vector<WebPluginGeometry>& moves) override;
   void Focus() override;
   void UpdateCursor(const WebCursor& cursor) override;
@@ skipping 565 matching lines @@
   float device_scale_factor_;
 
   base::WeakPtrFactory<RenderWidgetHostViewAura> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewAura);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_AURA_H_