Aura: Allow browser UI thread waiting for compositor commits.

cc/CCCompletionEvent.h

 // Copyright 2011 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.
 
 #ifndef CCCompletionEvent_h
 #define CCCompletionEvent_h
 
 #include "base/synchronization/waitable_event.h"
+#include "base/threading/thread_restrictions.h"
 
 namespace cc {
 
 // Used for making blocking calls from one thread to another. Use only when
 // absolutely certain that doing-so will not lead to a deadlock.
 //
 // It is safe to destroy this object as soon as wait() returns.
 class CCCompletionEvent {
 public:
     CCCompletionEvent()
@@ skipping 10 matching lines @@
         ASSERT(m_waited);
         ASSERT(m_signaled);
     }
 
     void wait()
     {
         ASSERT(!m_waited);
 #ifndef NDEBUG
         m_waited = true;
 #endif
+        base::ThreadRestrictions::ScopedAllowWait allow_wait;
         m_event.Wait();
     }
 
     void signal()
     {
         ASSERT(!m_signaled);
 #ifndef NDEBUG
         m_signaled = true;
 #endif
         m_event.Signal();
     }
 
 private:
     base::WaitableEvent m_event;
 #ifndef NDEBUG
     // Used to assert that wait() and signal() are each called exactly once.
     bool m_waited;
     bool m_signaled;
 #endif
 };
 
 }
 
 #endif