Standardize usage of virtual/override/final in base/

BUG=417463
TBR=danakj@chromium.org

Review URL: https://codereview.chromium.org/668783004

Cr-Commit-Position: refs/heads/master@{#300447}


CrOS-Libchrome-Original-Commit: 5648818ef9d5ef5fda79cd5dde2e42567af07785
diff --git a/base/message_loop/message_loop.h b/base/message_loop/message_loop.h
index a180cc3..b781711 100644
--- a/base/message_loop/message_loop.h
+++ b/base/message_loop/message_loop.h
@@ -115,7 +115,7 @@
   // Creates a TYPE_CUSTOM MessageLoop with the supplied MessagePump, which must
   // be non-NULL.
   explicit MessageLoop(scoped_ptr<base::MessagePump> pump);
-  virtual ~MessageLoop();
+  ~MessageLoop() override;
 
   // Returns the MessageLoop object for the current thread, or null if none.
   static MessageLoop* current();
@@ -442,9 +442,9 @@
   void HistogramEvent(int event);
 
   // MessagePump::Delegate methods:
-  virtual bool DoWork() override;
-  virtual bool DoDelayedWork(TimeTicks* next_delayed_work_time) override;
-  virtual bool DoIdleWork() override;
+  bool DoWork() override;
+  bool DoDelayedWork(TimeTicks* next_delayed_work_time) override;
+  bool DoIdleWork() override;
 
   const Type type_;