Add builders for tracing event's structural arguments

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index e602872ba63921178b883395d16b37c1a33d8120..fa6d63a978dcd91511b5ae2cb610a154c33958d2 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -28,6 +28,12 @@ struct hash<cc::LayerImpl*> {
 }  // namespace BASE_HASH_NAMESPACE
 #endif  // COMPILER
 
+namespace base {
+namespace debug {
+class TracedValue;
+}
+}
+
 namespace cc {
 
 class ContextProvider;
@@ -106,7 +112,7 @@ class CC_EXPORT LayerTreeImpl {
   const LayerTreeDebugState& debug_state() const;
   float device_scale_factor() const;
   DebugRectHistory* debug_rect_history() const;
-  scoped_ptr<base::Value> AsValue() const;
+  void AsValueInto(base::debug::TracedValue* dict) const;
 
   // Other public methods
   // ---------------------------------------------------------------------------