Revert of Assert sequence validity on non-thread-safe RefCount manipulations (2)

cc/trees/proxy_impl.cc

Index: cc/trees/proxy_impl.cc
diff --git a/cc/trees/proxy_impl.cc b/cc/trees/proxy_impl.cc
index 39040a4a9f7ab5528fdf64406211dc6d94b7587b..3817b28fa3cfc65a6c9eb2142a86cd7bce63ea98 100644
--- a/cc/trees/proxy_impl.cc
+++ b/cc/trees/proxy_impl.cc
@@ -495,12 +495,6 @@
   DCHECK(IsMainThreadBlocked());
   DCHECK(commit_completion_event_);
 
-  // Relax the cross-thread access restriction to non-thread-safe RefCount.
-  // It's safe since the main thread is blocked while a main-thread-bound
-  // compositor stuff are accessed from the impl thread.
-  base::ScopedAllowCrossThreadRefCountAccess
-      allow_cross_thread_ref_count_access;
-
   layer_tree_host_impl_->BeginCommit();
   blocked_main_commit().layer_tree_host->FinishCommitOnImplThread(
       layer_tree_host_impl_.get());