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

cc/trees/proxy_impl.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/proxy_impl.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/auto_reset.h"
@@ skipping 477 matching lines @@
   bool forced_draw = true;
   return DrawInternal(forced_draw);
 }
 
 void ProxyImpl::ScheduledActionCommit() {
   TRACE_EVENT0("cc", "ProxyImpl::ScheduledActionCommit");
   DCHECK(IsImplThread());
   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());
 
   // Remove the LayerTreeHost reference before the completion event is signaled
   // and cleared. This is necessary since blocked_main_commit() allows access
   // only while we have the completion event to ensure the main thread is
   // blocked for a commit.
   blocked_main_commit().layer_tree_host = nullptr;
 
@@ skipping 135 matching lines @@
 ProxyImpl::BlockedMainCommitOnly& ProxyImpl::blocked_main_commit() {
   DCHECK(IsMainThreadBlocked() && commit_completion_event_);
   return main_thread_blocked_commit_vars_unsafe_;
 }
 
 base::SingleThreadTaskRunner* ProxyImpl::MainThreadTaskRunner() {
   return task_runner_provider_->MainThreadTaskRunner();
 }
 
 }  // namespace cc