Allow to have a transparent UA dependent background.

content/browser/renderer_host/render_widget_host_view_base.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_BASE_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_BASE_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 67 matching lines @@
  public:
   ~RenderWidgetHostViewBase() override;
 
   float current_device_scale_factor() const {
     return current_device_scale_factor_;
   }
 
   // RenderWidgetHostView implementation.
   void SetBackgroundColor(SkColor color) override;
   void SetBackgroundColorToDefault() final;
+  void SetBackgroundOpaque(bool opaque) override;
   bool GetBackgroundOpaque() override;
   ui::TextInputClient* GetTextInputClient() override;
   void WasUnOccluded() override {}
   void WasOccluded() override {}
   bool IsShowingContextMenu() const override;
   void SetShowingContextMenu(bool showing_menu) override;
   base::string16 GetSelectedText() const override;
   bool IsMouseLocked() override;
   gfx::Size GetVisibleViewportSize() const override;
   void SetInsets(const gfx::Insets& insets) override;
@@ skipping 323 matching lines @@
   static void DetachPluginsHelper(HWND parent);
 #endif
 
   // Whether this view is a popup and what kind of popup it is (select,
   // autofill...).
   blink::WebPopupType popup_type_;
 
   // The background color of the web content.
   SkColor background_color_;
 
+  // The background transparency of the web content.
+  bool background_opaque_;
+
   // While the mouse is locked, the cursor is hidden from the user. Mouse events
   // are still generated. However, the position they report is the last known
   // mouse position just as mouse lock was entered; the movement they report
   // indicates what the change in position of the mouse would be had it not been
   // locked.
   bool mouse_locked_;
 
   // Whether we are showing a context menu.
   bool showing_context_menu_;
 
@@ skipping 30 matching lines @@
   base::ObserverList<RenderWidgetHostViewBaseObserver> observers_;
 
   base::WeakPtrFactory<RenderWidgetHostViewBase> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewBase);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_BASE_H_