Enable strict-virtual-specifiers for iOS builds.

base/message_loop/message_pump_mac.h

Index: base/message_loop/message_pump_mac.h
diff --git a/base/message_loop/message_pump_mac.h b/base/message_loop/message_pump_mac.h
index 55ab2c674d48179190141a4ebecd1e077569f26f..c8532020847e287159401420ed2d81df7bdd4645 100644
--- a/base/message_loop/message_pump_mac.h
+++ b/base/message_loop/message_pump_mac.h
@@ -263,9 +263,9 @@ class BASE_EXPORT MessagePumpNSRunLoop : public MessagePumpCFRunLoopBase {
 class MessagePumpUIApplication : public MessagePumpCFRunLoopBase {
  public:
   MessagePumpUIApplication();
-  virtual ~MessagePumpUIApplication();
-  virtual void DoRun(Delegate* delegate) override;
-  virtual void Quit() override;
+  ~MessagePumpUIApplication() override;
+  void DoRun(Delegate* delegate) override;
+  void Quit() override;
 
   // This message pump can not spin the main message loop directly.  Instead,
   // call |Attach()| to set up a delegate.  It is an error to call |Run()|.