Add virtual and OVERRIDE to base/ implementation files

base/synchronization/waitable_event_unittest.cc

Index: base/synchronization/waitable_event_unittest.cc
diff --git a/base/synchronization/waitable_event_unittest.cc b/base/synchronization/waitable_event_unittest.cc
index f25326550e4b81993e9f8c79c86d6a62d2e59c8c..01cfe69a1634c964a4bda5bc04f7489a76376acd 100644
--- a/base/synchronization/waitable_event_unittest.cc
+++ b/base/synchronization/waitable_event_unittest.cc
@@ -2,8 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "base/time.h"
 #include "base/synchronization/waitable_event.h"
+
+#include "base/compiler_specific.h"
+#include "base/time.h"
 #include "base/threading/platform_thread.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
@@ -76,7 +78,7 @@ class WaitableEventSignaler : public PlatformThread::Delegate {
         ev_(ev) {
   }
 
-  void ThreadMain() {
+  virtual void ThreadMain() OVERRIDE {
     PlatformThread::Sleep(TimeDelta::FromSeconds(static_cast<int>(seconds_)));
     ev_->Signal();
   }