Use SaveLayerAlpha bounds when doing Save-Draw-Restore optimization

cc/paint/display_item_list.cc

 // Copyright 2014 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 "cc/paint/display_item_list.h"
 
 #include <stddef.h>
 
 #include <string>
 
@@ skipping 165 matching lines @@
   // relevant here and that lcd text is preserved post merge, but I haven't
   // tested that.
   const PaintRecord* record = draw_item.picture.get();
   if (record->size() != 1u)
     return false;
 
   const PaintOp* op = record->GetFirstOp();
   if (!op->IsDrawOp())
     return false;
 
-  op->RasterWithAlpha(canvas, save_item.alpha);
+  SkRect bounds = save_item.has_bounds ? save_item.bounds : PaintOp::kUnsetRect;
+  op->RasterWithAlpha(canvas, bounds, save_item.alpha);
   return true;
 }
 
 void DisplayItemList::Raster(SkCanvas* canvas,
                              SkPicture::AbortCallback* callback) const {
   gfx::Rect canvas_playback_rect;
   if (!GetCanvasClipBounds(canvas, &canvas_playback_rect))
     return;
 
   std::vector<size_t> indices = rtree_.Search(canvas_playback_rect);
@@ skipping 339 matching lines @@
     std::vector<DrawImage>* images) {
   image_map_.GetDiscardableImagesInRect(rect, contents_scale,
                                         target_color_space, images);
 }
 
 gfx::Rect DisplayItemList::GetRectForImage(PaintImage::Id image_id) const {
   return image_map_.GetRectForImage(image_id);
 }
 
 }  // namespace cc