Add virtual and OVERRIDE to base/ implementation files

base/memory/weak_ptr_unittest.cc

Index: base/memory/weak_ptr_unittest.cc
diff --git a/base/memory/weak_ptr_unittest.cc b/base/memory/weak_ptr_unittest.cc
index 8f42664ee244a486b433b70837d2722d477a87ec..f2e53ef2c7f1afbfc2e1378d5052f065f34c1a71 100644
--- a/base/memory/weak_ptr_unittest.cc
+++ b/base/memory/weak_ptr_unittest.cc
@@ -44,11 +44,9 @@ struct Consumer { WeakPtr<Producer> producer; };
 // and delete objects on a background thread.
 class BackgroundThread : public Thread {
  public:
-  BackgroundThread()
-      : Thread("owner_thread") {
-  }
+  BackgroundThread() : Thread("owner_thread") {}
 
-  ~BackgroundThread() {
+  virtual ~BackgroundThread() {
     Stop();
   }