Add virtual and OVERRIDE to base/ implementation files

base/synchronization/waitable_event_watcher_posix.cc

Index: base/synchronization/waitable_event_watcher_posix.cc
diff --git a/base/synchronization/waitable_event_watcher_posix.cc b/base/synchronization/waitable_event_watcher_posix.cc
index 3b0ba70c22b481891d49dea8b3f9437b0ae17084..c45792d240347be010d6a548298df013e3dbef38 100644
--- a/base/synchronization/waitable_event_watcher_posix.cc
+++ b/base/synchronization/waitable_event_watcher_posix.cc
@@ -43,6 +43,9 @@ class Flag : public RefCountedThreadSafe<Flag> {
   }
 
  private:
+  friend class RefCountedThreadSafe<Flag>;
+  ~Flag() {}
+
   mutable Lock lock_;
   bool flag_;
 };
@@ -60,7 +63,7 @@ class AsyncWaiter : public WaitableEvent::Waiter {
         callback_(callback),
         flag_(flag) { }
 
-  bool Fire(WaitableEvent* event) {
+  virtual bool Fire(WaitableEvent* event) OVERRIDE {
     // Post the callback if we haven't been cancelled.
     if (!flag_->value()) {
       message_loop_->PostTask(FROM_HERE, callback_);
@@ -76,7 +79,7 @@ class AsyncWaiter : public WaitableEvent::Waiter {
   }
 
   // See StopWatching for discussion
-  bool Compare(void* tag) {
+  virtual bool Compare(void* tag) OVERRIDE {
     return tag == flag_.get();
   }