Allow CopyFromBackingStore to fallback to copying from the renderer side if the accelerated surface…

content/public/browser/render_widget_host.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_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_
 #define CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_
 
 #include "base/callback.h"
 #include "content/common/content_export.h"
 #include "content/public/browser/keyboard_listener.h"
@@ skipping 165 matching lines @@
   // bitmap to a callback.
   //
   // If |src_rect| is empty, the whole contents is copied. If non empty
   // |accelerated_dst_size| is given and accelerated compositing is active, the
   // content is shrunk so that it fits in |accelerated_dst_size|. If
   // |accelerated_dst_size| is larger than the content size, the content is not
   // resized. If |accelerated_dst_size| is empty, the size copied from the
   // source contents is used. |callback| is invoked with true on success, false
   // otherwise, along with a SkBitmap containing the copied pixel data.
   //
+  // If the backing store is not available or, in composited mode, the
+  // accelerated surface is not available to the browser, then the copy is done
+  // on the renderer side via IPC.
+  //
   // NOTE: |callback| is called synchronously if the backing store is available.
   // When accelerated compositing is active, |callback| may be called
   // asynchronously.
   virtual void CopyFromBackingStore(
       const gfx::Rect& src_rect,
       const gfx::Size& accelerated_dst_size,
       const base::Callback<void(bool, const SkBitmap&)>& callback) = 0;
 #if defined(TOOLKIT_GTK)
   // Paint the backing store into the target's |dest_rect|.
   virtual bool CopyFromBackingStoreToGtkWindow(const gfx::Rect& dest_rect,
@@ skipping 95 matching lines @@
   // within content/.  This method is necessary because
   // RenderWidgetHost is the root of a diamond inheritance pattern, so
   // subclasses inherit it virtually, which removes our ability to
   // static_cast to the subclass.
   virtual RenderWidgetHostImpl* AsRenderWidgetHostImpl() = 0;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_RENDER_WIDGET_HOST_H_