cc: Use pointers for heaps in tile manager raster tile priority queue.

cc/resources/raster_tile_priority_queue.h

Index: cc/resources/raster_tile_priority_queue.h
diff --git a/cc/resources/raster_tile_priority_queue.h b/cc/resources/raster_tile_priority_queue.h
index 7c028d1d81fa545f5badf4855230b9b7db91e4f9..0e2bcf65b0276aa90b2e2754625623c1b3d4254c 100644
--- a/cc/resources/raster_tile_priority_queue.h
+++ b/cc/resources/raster_tile_priority_queue.h
@@ -47,7 +47,10 @@ class CC_EXPORT RasterTilePriorityQueue {
   void Pop();
 
  private:
-  std::vector<PairedPictureLayerQueue> paired_queues_;
+  // TODO(vmpstr): This is potentially unnecessary if it becomes the case that
+  // PairedPictureLayerQueue is fast enough to copy. In that case, we can use
+  // objects directly (ie std::vector<PairedPictureLayerQueue>.
+  ScopedPtrVector<PairedPictureLayerQueue> paired_queues_heap_;
   TreePriority tree_priority_;
 
   DISALLOW_COPY_AND_ASSIGN(RasterTilePriorityQueue);