cc: Cancel RenewTreePriorirty callback if LTHI is gone.

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index 4a95140226db8fd2c72da44e632ebdd880bf1f5e..af1cd3b9cab7e6c260043ce156007f2d04c5c312 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -1254,6 +1254,12 @@ void ThreadProxy::LayerTreeHostClosedOnImplThread(CompletionEvent* completion) {
   impl().scheduler.reset();
   impl().layer_tree_host_impl.reset();
   impl().weak_factory.InvalidateWeakPtrs();
+  // We need to explicitly cancel the notifier, since it isn't using weak ptrs.
+  // TODO(vmpstr): We should see if we can make it use weak ptrs and still keep
+  // the convention of having a weak ptr factory initialized last. Alternatively
+  // we should moved the notifier (and RenewTreePriority) to LTHI. See
+  // crbug.com/411972
+  impl().smoothness_priority_expiration_notifier.Cancel();
   impl().contents_texture_manager = NULL;
   completion->Signal();
 }