Add TRACE_EVENT_IS_NEW_TRACE as a way to snapshot objects at start of recording

cc/resources/picture.h

Index: cc/resources/picture.h
diff --git a/cc/resources/picture.h b/cc/resources/picture.h
index 5e4e5ca8bd9d5fb1639bce3fdcafb21e7586e4a3..c877b269c96bfa5d49dd4f7678fcb7b153cf919b 100644
--- a/cc/resources/picture.h
+++ b/cc/resources/picture.h
@@ -78,6 +78,7 @@ class CC_EXPORT Picture
               bool enable_lcd_text);
 
   scoped_ptr<base::Value> AsValue() const;
+  void DidBeginTracing();
 
   class CC_EXPORT PixelRefIterator {
    public:
@@ -137,6 +138,7 @@ class CC_EXPORT Picture
 
   scoped_ptr<base::debug::ConvertableToTraceFormat>
     AsTraceableRasterData(gfx::Rect rect, float scale);
+  void EmitTraceSnapshot();
 
   friend class base::RefCountedThreadSafe<Picture>;
   friend class PixelRefIterator;