[WIP] cc: Use reverse spiral iterator in tiling eviction.

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 e91f0d2a682dc7e140bf40baeeaf334dc61b9d90..bae8f86745ea0a6803c6a225452ee71914236d74 100644
--- a/cc/resources/eviction_tile_priority_queue.h
+++ b/cc/resources/eviction_tile_priority_queue.h
@@ -5,6 +5,7 @@
 #ifndef CC_RESOURCES_EVICTION_TILE_PRIORITY_QUEUE_H_
 #define CC_RESOURCES_EVICTION_TILE_PRIORITY_QUEUE_H_
 
+#include <set>
 #include <utility>
 #include <vector>
 
@@ -31,8 +32,8 @@ class CC_EXPORT EvictionTilePriorityQueue {
     PictureLayerImpl::LayerEvictionTileIterator active_iterator;
     PictureLayerImpl::LayerEvictionTileIterator pending_iterator;
 
-    // TODO(vmpstr): Investigate removing this.
-    std::vector<Tile*> returned_shared_tiles;
+    // Set of returned tiles (excluding the current one) for DCHECKing.
+    std::set<const Tile*> returned_tiles_for_debug;
   };
 
   EvictionTilePriorityQueue();