Trace picture piles on layers

cc/resources/picture_pile_base.cc

Index: cc/resources/picture_pile_base.cc
diff --git a/cc/resources/picture_pile_base.cc b/cc/resources/picture_pile_base.cc
index 897ed2cbe7a4ea6b4dd62fb5f22b4978538f0221..85c2ee888ecbbdd081a986d41516e3133fa838bd 100644
--- a/cc/resources/picture_pile_base.cc
+++ b/cc/resources/picture_pile_base.cc
@@ -8,6 +8,9 @@
 #include <vector>
 
 #include "base/logging.h"
+#include "base/values.h"
+#include "cc/base/math_util.h"
+#include "cc/debug/traced_value.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/gfx/rect_conversions.h"
 
@@ -173,4 +176,25 @@ bool PicturePileBase::CanRaster(float contents_scale, gfx::Rect content_rect) {
   return recorded_region_.Contains(layer_rect);
 }
 
+scoped_ptr<base::Value> PicturePileBase::AsValue() const {
+  scoped_ptr<base::ListValue> pictures(new base::ListValue());
+  gfx::Rect layer_rect(tiling_.total_size());
+  for (TilingData::Iterator tile_iter(&tiling_, layer_rect);
+       tile_iter; ++tile_iter) {
+    PictureListMap::const_iterator map_iter =
+        picture_list_map_.find(tile_iter.index());
+    if (map_iter == picture_list_map_.end())
+      continue;
+    const PictureList& pic_list= map_iter->second;
+    if (pic_list.empty())
+      continue;
+    for (PictureList::const_reverse_iterator i = pic_list.rbegin();
+         i != pic_list.rend(); ++i) {
+      Picture* picture = (*i).get();
+      pictures->Append(TracedValue::CreateIDRef(picture).release());
+    }
+  }
+  return pictures.PassAs<base::Value>();
+}
+
 }  // namespace cc