Retain references to surfaces from both active AND pending CompositorFrames

cc/surfaces/surface.h

Index: cc/surfaces/surface.h
diff --git a/cc/surfaces/surface.h b/cc/surfaces/surface.h
index a427a8224fc45eb142d1b30e558c5d38dac50392..278e021f13182581e7c8c3a204424a99de7c9909 100644
--- a/cc/surfaces/surface.h
+++ b/cc/surfaces/surface.h
@@ -105,6 +105,10 @@ class CC_SURFACES_EXPORT Surface {
     return referenced_surfaces_;
   }
 
+  const std::vector<SurfaceId>& pending_referenced_surfaces() const {
+    return pending_referenced_surfaces_;
+  }
+
   const SurfaceDependencies& blocking_surfaces_for_testing() const {
     return blocking_surfaces_;
   }
@@ -143,6 +147,9 @@ class CC_SURFACES_EXPORT Surface {
   // The total set of CompositorFrames referenced by the active CompositorFrame.
   std::vector<SurfaceId> referenced_surfaces_;
 
+  // The total set of SurfaceIds referenced by the pending CompositorFrame.
+  std::vector<SurfaceId> pending_referenced_surfaces_;
+
   SurfaceDependencies blocking_surfaces_;
   base::ObserverList<PendingFrameObserver, true> observers_;