win: Fix a few clang style plugin warnings.

base/win/object_watcher.h

Index: base/win/object_watcher.h
diff --git a/base/win/object_watcher.h b/base/win/object_watcher.h
index 0ae253294201f9acdbfa4fea6220eabf8639cb93..d68d9350b3860f83ae726fc83d3cbbd75618aedc 100644
--- a/base/win/object_watcher.h
+++ b/base/win/object_watcher.h
@@ -56,7 +56,7 @@ class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver {
   };
 
   ObjectWatcher();
-  ~ObjectWatcher();
+  ~ObjectWatcher() override;
 
   // When the object is signaled, the given delegate is notified on the thread
   // where StartWatching is called.  The ObjectWatcher is not responsible for
@@ -87,7 +87,7 @@ class BASE_EXPORT ObjectWatcher : public MessageLoop::DestructionObserver {
   void Signal(Delegate* delegate);
 
   // MessageLoop::DestructionObserver implementation:
-  virtual void WillDestroyCurrentMessageLoop();
+  void WillDestroyCurrentMessageLoop() override;
 
   // Internal state.
   Closure callback_;