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

cc/tiles/tile_manager.cc

 // Copyright 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 "cc/tiles/tile_manager.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 862 matching lines @@
 
   // Create and queue all image decode tasks that this tile depends on.
   ImageDecodeTask::Vector decode_tasks;
   std::vector<DrawImage>& images = scheduled_draw_images_[tile->id()];
   images.clear();
   if (!playback_settings.skip_images) {
     prioritized_tile.raster_source()->GetDiscardableImagesInRect(
         tile->enclosing_layer_rect(), tile->contents_scale(), &images);
   }
 
-  // TODO(vmpstr): We should disable image hijack canvas in
-  // |playback_settings| here if |images| is empty.
-
+  // We can skip the image hijack canvas if we have no images.
+  playback_settings.use_image_hijack_canvas = !images.empty();
   for (auto it = images.begin(); it != images.end();) {
     scoped_refptr<ImageDecodeTask> task;
     bool need_to_unref_when_finished =
         image_decode_controller_->GetTaskForImageAndRef(
             *it, prepare_tiles_count_, &task);
     if (task)
       decode_tasks.push_back(task);
 
     if (need_to_unref_when_finished)
       ++it;
@@ skipping 340 matching lines @@
 void TileManager::Signals::reset() {
   ready_to_activate = false;
   did_notify_ready_to_activate = false;
   ready_to_draw = false;
   did_notify_ready_to_draw = false;
   all_tile_tasks_completed = false;
   did_notify_all_tile_tasks_completed = false;
 }
 
 }  // namespace cc