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

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index b6a4120eb63c39bc0dd770137d9e6c3004d5d507..36fa9e488c5ce71020be88a368c88d8726146dfd 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -946,6 +946,15 @@ Region LayerImpl::VisibleContentOpaqueRegion() const {
   return Region();
 }
 
+void LayerImpl::DidBeginTracing() {

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

No more roll-your-own-layer-recursion.  Please use CallFunctionForSubtree.  See
also: https://codereview.chromium.org/15959012/

+  for (size_t i = 0; i < children_.size(); ++i)
+    children_[i]->DidBeginTracing();
+  if (mask_layer_)
+    mask_layer_->DidBeginTracing();
+  if (replica_layer_)
+    replica_layer_->DidBeginTracing();
+}
+
 void LayerImpl::DidLoseOutputSurface() {}
 
 void LayerImpl::SetMaxScrollOffset(gfx::Vector2d max_scroll_offset) {