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

cc/resources/picture.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_H_
 #define CC_RESOURCES_PICTURE_H_
 
 #include <string>
 #include <utility>
 #include <vector>
@@ skipping 60 matching lines @@
   bool HasRecording() const { return picture_.get() != NULL; }
 
   // Apply this contents scale and raster the content rect into the canvas.
   void Raster(SkCanvas* canvas,
               SkDrawPictureCallback* callback,
               gfx::Rect content_rect,
               float contents_scale,
               bool enable_lcd_text);
 
   scoped_ptr<base::Value> AsValue() const;
+  void DidBeginTracing();
 
   class CC_EXPORT PixelRefIterator {
    public:
     PixelRefIterator();
     PixelRefIterator(gfx::Rect layer_rect, const Picture* picture);
     ~PixelRefIterator();
 
     skia::LazyPixelRef* operator->() const {
       DCHECK_LT(current_index_, current_pixel_refs_->size());
       return (*current_pixel_refs_)[current_index_];
@@ skipping 48 matching lines @@
     AsTraceableRasterData(gfx::Rect rect, float scale);
 
   friend class base::RefCountedThreadSafe<Picture>;
   friend class PixelRefIterator;
   DISALLOW_COPY_AND_ASSIGN(Picture);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_PICTURE_H_