Support different formats in the same resource pool.

cc/resources/tile.h

Index: cc/resources/tile.h
diff --git a/cc/resources/tile.h b/cc/resources/tile.h
index 2394dcb6be11cab18a319f39ec3682943e28485b..6c6713f0e6232db88755c7fc516ab11dc0525813 100644
--- a/cc/resources/tile.h
+++ b/cc/resources/tile.h
@@ -19,7 +19,7 @@ class TileManager;
 
 class CC_EXPORT Tile : public RefCountedManaged<Tile> {
  public:
-  enum TileRasterFlags { USE_PICTURE_ANALYSIS = 1 << 0 };
+  enum TileRasterFlags { USE_PICTURE_ANALYSIS = 1 << 0, IS_OPAQUE = 1 << 1 };
 
   typedef uint64 Id;
 
@@ -106,6 +106,8 @@ class CC_EXPORT Tile : public RefCountedManaged<Tile> {
 
   inline bool IsReadyToDraw() const { return draw_info_.IsReadyToDraw(); }
 
+  bool IsOpaque() const { return !!(flags_ & IS_OPAQUE); }
+
   const TileDrawInfo& draw_info() const { return draw_info_; }
 
   TileDrawInfo& draw_info() { return draw_info_; }