Add virtual and OVERRIDE to base/ implementation files

base/synchronization/waitable_event_posix.cc

Index: base/synchronization/waitable_event_posix.cc
diff --git a/base/synchronization/waitable_event_posix.cc b/base/synchronization/waitable_event_posix.cc
index 01077ff3bea2a820dc21a4d493152b0911c70cd0..fbf8d100ce7c8419f2feccde60b62734befff6d3 100644
--- a/base/synchronization/waitable_event_posix.cc
+++ b/base/synchronization/waitable_event_posix.cc
@@ -91,7 +91,7 @@ class SyncWaiter : public WaitableEvent::Waiter {
         cv_(&lock_) {
   }
 
-  bool Fire(WaitableEvent* signaling_event) {
+  virtual bool Fire(WaitableEvent* signaling_event) OVERRIDE {
     base::AutoLock locked(lock_);
 
     if (fired_)
@@ -117,7 +117,7 @@ class SyncWaiter : public WaitableEvent::Waiter {
   // These waiters are always stack allocated and don't delete themselves. Thus
   // there's no problem and the ABA tag is the same as the object pointer.
   // ---------------------------------------------------------------------------
-  bool Compare(void* tag) {
+  virtual bool Compare(void* tag) OVERRIDE {
     return this == tag;
   }