Support browser side thumbnailing for GPU composited pages on Windows.

chrome/browser/tab_contents/thumbnail_generator.cc

 // 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.
 
 #include "chrome/browser/tab_contents/thumbnail_generator.h"
 
 #include <algorithm>
 #include <map>
 
 #include "base/bind.h"
@@ skipping 59 matching lines @@
     int desired_height,
     int options,
     ThumbnailGenerator::ClipResult* clip_result) {
   base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
 
   SkBitmap result;
 
   // Get the bitmap as a Skia object so we can resample it. This is a large
   // allocation and we can tolerate failure here, so give up if the allocation
   // fails.
+  // TODO(mazda): Copy a shrinked size of image instead of the whole view size.
   skia::PlatformCanvas temp_canvas;
-  if (!render_widget_host->CopyFromBackingStore(&temp_canvas))
+  if (!render_widget_host->CopyFromBackingStore(gfx::Size(), &temp_canvas))
     return result;
   const SkBitmap& bmp_with_scrollbars =
       skia::GetTopDevice(temp_canvas)->accessBitmap(false);
   // Clip the edgemost 15 pixels as that will commonly hold a scrollbar, which
   // looks bad in thumbnails.
   SkIRect scrollbarless_rect =
       { 0, 0,
         std::max(1, bmp_with_scrollbars.width() - 15),
         std::max(1, bmp_with_scrollbars.height() - 15) };
   SkBitmap bmp;
@@ skipping 420 matching lines @@
 
 void ThumbnailGenerator::DidStartLoading() {
   load_interrupted_ = false;
 }
 
 void ThumbnailGenerator::StopNavigation() {
   // This function gets called when the page loading is interrupted by the
   // stop button.
   load_interrupted_ = true;
 }