Early out from CleanUpUnusedImageDecodeTasks().

cc/resources/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/resources/tile_manager.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 
@@ skipping 608 matching lines @@
       global_state_.memory_limit_in_bytes;
   memory_stats_from_last_assign_.bytes_allocated =
       bytes_allocatable - bytes_left;
   memory_stats_from_last_assign_.bytes_unreleasable =
       bytes_allocatable - bytes_releasable_;
   memory_stats_from_last_assign_.bytes_over =
       bytes_that_exceeded_memory_budget;
 }
 
 void TileManager::CleanUpUnusedImageDecodeTasks() {
+  if (image_decode_tasks_.empty())
+    return;
+
   // Calculate a set of layers that are used by at least one tile.
   base::hash_set<int> used_layers;
   for (TileMap::iterator it = tiles_.begin(); it != tiles_.end(); ++it)
     used_layers.insert(it->second->layer_id());
 
   // Now calculate the set of layers in |image_decode_tasks_| that are not used
   // by any tile.
   std::vector<int> unused_layers;
   for (LayerPixelRefTaskMap::iterator it = image_decode_tasks_.begin();
        it != image_decode_tasks_.end();
@@ skipping 209 matching lines @@
     bytes_releasable_ += tile->bytes_consumed_if_allocated();
     ++resources_releasable_;
   }
 
   FreeUnusedResourcesForTile(tile);
   if (tile->priority(ACTIVE_TREE).distance_to_visible_in_pixels == 0)
     did_initialize_visible_tile_ = true;
 }
 
 }  // namespace cc