Surface synchronization: Immediately activate late arriving CompositorFrames

cc/surfaces/surface_dependency_tracker.h

Index: cc/surfaces/surface_dependency_tracker.h
diff --git a/cc/surfaces/surface_dependency_tracker.h b/cc/surfaces/surface_dependency_tracker.h
index 7643574de3edc36cc230d16747e4105c596e32f2..bdb8717fd060c5a654bc14d80e0a6e2a8928c57f 100644
--- a/cc/surfaces/surface_dependency_tracker.h
+++ b/cc/surfaces/surface_dependency_tracker.h
@@ -87,6 +87,10 @@ class CC_SURFACES_EXPORT SurfaceDependencyTracker : public BeginFrameObserver,
   // blockers.
   base::flat_set<SurfaceId> observed_surfaces_by_id_;
 
+  // The set of SurfaceIds to which corresponding CompositorFrames have not
+  // arrived by the time their deadline fired.
+  base::flat_set<SurfaceId> late_surfaces_by_id_;
+
   DISALLOW_COPY_AND_ASSIGN(SurfaceDependencyTracker);
 };