cc: Separate the priority from the tile and put in new PrioritizedTile

cc/resources/eviction_tile_priority_queue.h

Index: cc/resources/eviction_tile_priority_queue.h
diff --git a/cc/resources/eviction_tile_priority_queue.h b/cc/resources/eviction_tile_priority_queue.h
index ecf3401ad001dcefa10ec0f79a6fcea4bae32acb..06118d987d99d86627bc72290c554ffaa5a54d82 100644
--- a/cc/resources/eviction_tile_priority_queue.h
+++ b/cc/resources/eviction_tile_priority_queue.h
@@ -15,6 +15,7 @@
 #include "cc/resources/tiling_set_eviction_queue.h"
 
 namespace cc {
+class PrioritizedTile;
 
 class CC_EXPORT EvictionTilePriorityQueue {
  public:
@@ -26,11 +27,12 @@ class CC_EXPORT EvictionTilePriorityQueue {
              TreePriority tree_priority);
 
   bool IsEmpty() const;
-  Tile* Top();
+  const PrioritizedTile& Top() const;
   void Pop();
 
  private:
   ScopedPtrVector<TilingSetEvictionQueue>& GetNextQueues();
+  const ScopedPtrVector<TilingSetEvictionQueue>& GetNextQueues() const;
 
   ScopedPtrVector<TilingSetEvictionQueue> active_queues_;
   ScopedPtrVector<TilingSetEvictionQueue> pending_queues_;