Trace picture piles on layers

cc/resources/picture_pile_base.h

Index: cc/resources/picture_pile_base.h
diff --git a/cc/resources/picture_pile_base.h b/cc/resources/picture_pile_base.h
index fdfff2bd75e40d7a37a91d58e7088a1a17b1d371..d1c5754313689da76b8af825efebfa54c557ab49 100644
--- a/cc/resources/picture_pile_base.h
+++ b/cc/resources/picture_pile_base.h
@@ -17,6 +17,10 @@
 #include "cc/resources/picture.h"
 #include "ui/gfx/size.h"
 
+namespace base {
+class Value;
+}
+
 namespace cc {
 
 class CC_EXPORT PicturePileBase : public base::RefCounted<PicturePileBase> {
@@ -41,6 +45,8 @@ class CC_EXPORT PicturePileBase : public base::RefCounted<PicturePileBase> {
   void SetTileGridSize(gfx::Size tile_grid_size);
   TilingData& tiling() { return tiling_; }
 
+  scoped_ptr<base::Value> AsValue() const;
+
  protected:
   virtual ~PicturePileBase();