Revert "Delete CC."

cc/base/completion_event.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 CC_BASE_COMPLETION_EVENT_H_
+#define CC_BASE_COMPLETION_EVENT_H_
+
+#include "base/logging.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 CompletionEvent {
+ public:
+  CompletionEvent()
+      : event_(false /* manual_reset */, false /* initially_signaled */) {
+#if DCHECK_IS_ON()
+    waited_ = false;
+    signaled_ = false;
+#endif
+  }
+
+  ~CompletionEvent() {
+#if DCHECK_IS_ON()
+    DCHECK(waited_);
+    DCHECK(signaled_);
+#endif
+  }
+
+  void Wait() {
+#if DCHECK_IS_ON()
+    DCHECK(!waited_);
+    waited_ = true;
+#endif
+    base::ThreadRestrictions::ScopedAllowWait allow_wait;
+    event_.Wait();
+  }
+
+  void Signal() {
+#if DCHECK_IS_ON()
+    DCHECK(!signaled_);
+    signaled_ = true;
+#endif
+    event_.Signal();
+  }
+
+ private:
+  base::WaitableEvent event_;
+#if DCHECK_IS_ON()
+  // Used to assert that Wait() and Signal() are each called exactly once.
+  bool waited_;
+  bool signaled_;
+#endif
+};
+
+}  // namespace cc
+
+#endif  // CC_BASE_COMPLETION_EVENT_H_