Update Native Client Authors to be Chromium Authors for the code moved from the

ppapi/native_client/src/shared/ppapi_proxy/browser_ppp_instance.cc

-// Copyright (c) 2011 The Native Client Authors. All rights reserved.
+// Copyright (c) 2011 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.
 
 #include "native_client/src/shared/ppapi_proxy/browser_ppp_instance.h"
 
 #include <stdio.h>
 #include <string.h>
 #include <limits>
 
 #include "native_client/src/include/checked_cast.h"
@@ skipping 153 matching lines @@
     DidCreate,
     DidDestroy,
     DidChangeView,
     DidChangeFocus,
     HandleDocumentLoad
   };
   return &instance_interface;
 }
 
 }  // namespace ppapi_proxy