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

cc/resources/picture.cc

Index: cc/resources/picture.cc
diff --git a/cc/resources/picture.cc b/cc/resources/picture.cc
index b0f3fa30e59f0587759f402efd64fd6fe71392da..102e8b7dd20e40513990047cfc6322961b43035d 100644
--- a/cc/resources/picture.cc
+++ b/cc/resources/picture.cc
@@ -225,8 +225,7 @@ void Picture::CloneForDrawing(int num_threads) {
                     pixel_refs_));
     clones_.push_back(clone);
 
-    TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
-      "cc::Picture", clone.get(), TracedPicture::AsTraceablePicture(clone));
+    clone->EmitTraceSnapshot();
   }
 }
 
@@ -273,8 +272,7 @@ void Picture::Record(ContentLayerClient* painter,
 
   opaque_rect_ = gfx::ToEnclosedRect(opaque_layer_rect);
 
-    TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
-      "cc::Picture", this, TracedPicture::AsTraceablePicture(this));
+  EmitTraceSnapshot();
 }
 
 void Picture::GatherPixelRefs(
@@ -388,6 +386,10 @@ scoped_ptr<Value> Picture::AsValue() const {
   return res.PassAs<base::Value>();
 }
 
+void Picture::DidBeginTracing() {

[enne (OOO), 2013/06/01 03:10:45]

I'm not sure this function really needs to exist.

+  EmitTraceSnapshot();
+}
+
 base::LazyInstance<Picture::PixelRefs>
     Picture::PixelRefIterator::empty_pixel_refs_;
 
@@ -498,4 +500,9 @@ scoped_ptr<base::debug::ConvertableToTraceFormat>
   return TracedValue::FromValue(raster_data.release());
 }
 
+void Picture::EmitTraceSnapshot() {
+  TRACE_EVENT_OBJECT_SNAPSHOT_WITH_ID(TRACE_DISABLED_BY_DEFAULT("cc.debug"),
+      "cc::Picture", this, TracedPicture::AsTraceablePicture(this));
+}
+
 }  // namespace cc