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 52 matching lines @@
 // Creates a downsampled thumbnail for the given RenderWidgetHost's backing
 // store. The returned bitmap will be isNull if there was an error creating it.
 SkBitmap GetBitmapForRenderWidgetHost(
     RenderWidgetHost* render_widget_host,
     int desired_width,
     int desired_height,
     int options,
     ThumbnailGenerator::ClipResult* clip_result) {
   base::TimeTicks begin_compute_thumbnail = base::TimeTicks::Now();
 
-  SkBitmap result;
+  bool is_accelerated_compositing_active = false;
+  content::RenderWidgetHostView* view = render_widget_host->view();
+  if (view) {
+    RenderWidgetHostImpl* rwhi = RenderWidgetHostImpl::FromRWHV(view);
+    is_accelerated_compositing_active =
+        rwhi->is_accelerated_compositing_active();
+  }
 
   // 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.
   skia::PlatformCanvas temp_canvas;
-  if (!render_widget_host->CopyFromBackingStore(&temp_canvas))
-    return result;
+  const bool copy_result = is_accelerated_compositing_active ?
+      render_widget_host->CopyFromCompositingSurface(&temp_canvas) :
+      render_widget_host->CopyFromBackingStore(&temp_canvas);
+  if (!copy_result)
+    return SkBitmap();
+
   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;
   bmp_with_scrollbars.extractSubset(&bmp, scrollbarless_rect);
 
+  SkBitmap result;
   // Check if a clipped thumbnail is requested.
   if (options & ThumbnailGenerator::kClippedThumbnail) {
     SkBitmap clipped_bitmap = ThumbnailGenerator::GetClippedBitmap(
         bmp, desired_width, desired_height, clip_result);
 
     // Need to resize it to the size we want, so downsample until it's
     // close, and let the caller make it the exact size if desired.
     result = SkBitmapOperations::DownsampleByTwoUntilSize(
         clipped_bitmap, desired_width, desired_height);
     // This is a bit subtle. SkBitmaps are refcounted, but the magic
@@ skipping 409 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;
 }