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

cc/resources/picture_pile_impl.cc

 // 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.
 
 #include <algorithm>
 #include <limits>
 
 #include "base/debug/trace_event.h"
 #include "cc/base/region.h"
 #include "cc/debug/debug_colors.h"
@@ skipping 359 matching lines @@
       pixel_ref_iterator_ = Picture::PixelRefIterator(
           layer_rect_,
           *picture_list_iterator_);
       if (pixel_ref_iterator_)
         return;
     }
     ++tile_iterator_;
   } while (AdvanceToTileWithPictures());
 }
 
+void PicturePileImpl::DidBeginTracing() {
+  gfx::Rect layer_rect(tiling_.total_size());
+  for (TilingData::Iterator tile_iter(&tiling_, layer_rect);

[enne (OOO), 2013/05/31 23:27:21]

It might be shorter to just iterate through the picture map and then each list
in the map.  No reason to use TilingData unless there's geometry involved.

+       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) {
+      (*i)->DidBeginTracing();
+    }
+  }
+}
+
 }  // namespace cc