NaCl: Fix Chromium style warnings in src/trusted/plugin/

ppapi/native_client/src/trusted/plugin/sel_ldr_launcher_chrome.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_NATIVE_CLIENT_SRC_TRUSTED_PLUGIN_SEL_LDR_LAUNCHER_CHROME_H_
 #define PPAPI_NATIVE_CLIENT_SRC_TRUSTED_PLUGIN_SEL_LDR_LAUNCHER_CHROME_H_
 
 #include "native_client/src/trusted/nonnacl_util/sel_ldr_launcher.h"
 #include "ppapi/c/pp_instance.h"
 #include "ppapi/c/private/ppb_nacl_private.h"
 #include "ppapi/cpp/completion_callback.h"
 
 namespace plugin {
 
 class SelLdrLauncherChrome : public nacl::SelLdrLauncherBase {
  public:
-  virtual bool Start(const char* url);
+  bool Start(const char* url) override;
 
   // Provides a way for LaunchSelLdr() to write bootstrap channel information
   // into this class.
   void set_channel(NaClHandle channel);
 };
 
 }  // namespace plugin
 
 #endif