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

cc/layers/picture_layer_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 "cc/layers/picture_layer_impl.h"
 
 #include <algorithm>
 
 #include "base/time.h"
 #include "cc/base/math_util.h"
@@ skipping 357 matching lines @@
   last_screen_space_transform_ = current_screen_space_transform;
   last_bounds_ = bounds();
   last_content_scale_ = contents_scale_x();
 }
 
 void PictureLayerImpl::DidBecomeActive() {
   LayerImpl::DidBecomeActive();
   tilings_->DidBecomeActive();
 }
 
+void PictureLayerImpl::DidBeginTracing() {
+  pile_->DidBeginTracing();
+}
+
 void PictureLayerImpl::DidLoseOutputSurface() {
   if (tilings_)
     tilings_->RemoveAllTilings();
 
   ResetRasterScale();
 }
 
 void PictureLayerImpl::CalculateContentsScale(
     float ideal_contents_scale,
     float device_scale_factor,
@@ skipping 626 matching lines @@
   state->Set("tilings", tilings_->AsValue().release());
   state->Set("pictures", pile_->AsValue().release());
   state->Set("invalidation", invalidation_.AsValue().release());
 }
 
 size_t PictureLayerImpl::GPUMemoryUsageInBytes() const {
   return tilings_->GPUMemoryUsageInBytes();
 }
 
 }  // namespace cc