cc: Disable image hijack canvas when tiles don't have images.

cc/playback/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/playback/display_item_list.h"
 
 #include <stddef.h>
 
 #include <string>
 
@@ skipping 290 matching lines @@
          gfx::Rect(layer_rect_.right(), layer_rect_.bottom()), 1.f);
 }
 
 void DisplayItemList::GetDiscardableImagesInRect(
     const gfx::Rect& rect,
     float raster_scale,
     std::vector<DrawImage>* images) {
   image_map_.GetDiscardableImagesInRect(rect, raster_scale, images);
 }
 
-bool DisplayItemList::MayHaveDiscardableImages() const {
-  return !image_map_.empty();
-}
-
 }  // namespace cc