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

cc/resources/picture_pile_impl.h

 // Copyright 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_RESOURCES_PICTURE_PILE_IMPL_H_
 #define CC_RESOURCES_PICTURE_PILE_IMPL_H_
 
 #include <list>
 #include <map>
 #include <vector>
@@ skipping 91 matching lines @@
     void AdvanceToPictureWithPixelRefs();
 
     const PicturePileImpl* picture_pile_;
     gfx::Rect layer_rect_;
     TilingData::Iterator tile_iterator_;
     Picture::PixelRefIterator pixel_ref_iterator_;
     const PictureList* picture_list_;
     PictureList::const_iterator picture_list_iterator_;
   };
 
+  void DidBeginTracing();
+
  protected:
   friend class PicturePile;
   friend class PixelRefIterator;
 
   explicit PicturePileImpl(bool enable_lcd_text);
   PicturePileImpl(const PicturePileBase* other, bool enable_lcd_text);
   virtual ~PicturePileImpl();
 
  private:
   class ClonesForDrawing {
@@ skipping 24 matching lines @@
   // instance.  This member variable must be last so that other member
   // variables have already been initialized and can be clonable.
   const ClonesForDrawing clones_for_drawing_;
 
   DISALLOW_COPY_AND_ASSIGN(PicturePileImpl);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_PILE_IMPL_H_