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

mojo/shell/app_child_process_host.h

Index: mojo/shell/app_child_process_host.h
diff --git a/mojo/shell/app_child_process_host.h b/mojo/shell/app_child_process_host.h
index 30e6b798a24e2881465b08951689354a8125fd99..f65e2a48f165dcb3c26d78a102e8b57b9d16166d 100644
--- a/mojo/shell/app_child_process_host.h
+++ b/mojo/shell/app_child_process_host.h
@@ -35,8 +35,8 @@ class AppChildProcessHost : public ChildProcessHost,
 
  private:
   // |ChildProcessHost::Delegate| methods:
-  virtual void WillStart() OVERRIDE;
-  virtual void DidStart(bool success) OVERRIDE;
+  virtual void WillStart() override;
+  virtual void DidStart(bool success) override;
 
   // Callback for |embedder::CreateChannel()|.
   void DidCreateChannel(embedder::ChannelInfo* channel_info);