Mojo: Convert OVERRIDE -> override in various subdirectories of mojo/.

mojo/shell/context.h

Index: mojo/shell/context.h
diff --git a/mojo/shell/context.h b/mojo/shell/context.h
index c49b68cb18918681c1d3852376b94201412a0f48..1f098c753d0c37e2c6b82f96f3d3d9a9bd015837 100644
--- a/mojo/shell/context.h
+++ b/mojo/shell/context.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/macros.h"
 #include "mojo/application_manager/application_manager.h"
 #include "mojo/shell/mojo_url_resolver.h"
 #include "mojo/shell/task_runners.h"
@@ -33,7 +34,7 @@ class Context : ApplicationManager::Delegate {
   void Init();
 
   // ApplicationManager::Delegate override.
-  virtual void OnApplicationError(const GURL& gurl) OVERRIDE;
+  virtual void OnApplicationError(const GURL& gurl) override;
 
   void Run(const GURL& url);
   ScopedMessagePipeHandle ConnectToServiceByName(