Turn overdraw metrics on only when about:tracing is recording.

cc/layer_tree_host.cc

Index: cc/layer_tree_host.cc
diff --git a/cc/layer_tree_host.cc b/cc/layer_tree_host.cc
index 07d25919130c69184427d5f9e1bdf6d492fe05f6..418a4509796b7faa97f58a9b7c7fa0f1740a8608 100644
--- a/cc/layer_tree_host.cc
+++ b/cc/layer_tree_host.cc
@@ -668,7 +668,7 @@ bool LayerTreeHost::paintLayerContents(const LayerList& renderSurfaceLayerList,
     typedef LayerIterator<Layer, LayerList, RenderSurface, LayerIteratorActions::FrontToBack> LayerIteratorType;
 
     bool needMoreUpdates = false;
-    bool recordMetricsForFrame = true; // FIXME: In the future, disable this when about:tracing is off.
+    bool recordMetricsForFrame = base::debug::TraceLog::GetInstance()->IsEnabled();
     OcclusionTracker occlusionTracker(m_rootLayer->renderSurface()->contentRect(), recordMetricsForFrame);
     occlusionTracker.setMinimumTrackingSize(m_settings.minimumOcclusionTrackingSize);