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

ppapi/native_client/src/shared/ppapi_proxy/plugin_ppb_graphics_2d.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/plugin_ppb_graphics_2d.h"
 
 #include <stdio.h>
 #include <string.h>
 #include "native_client/src/include/portability.h"
 #include "native_client/src/shared/ppapi_proxy/plugin_callback.h"
 #include "native_client/src/shared/ppapi_proxy/plugin_globals.h"
@@ skipping 162 matching lines @@
     Describe,
     PaintImageData,
     Scroll,
     ReplaceContents,
     Flush,
   };
   return &graphics_2d_interface;
 }
 
 }  // namespace ppapi_proxy