Make the root_namespace argument to json_schema_compiler.gypi a string

extensions/shell/common/api/api.gyp

 # Copyright 2014 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.
 
 {
   'targets': [
     {
       'target_name': 'shell_api',
       'type': 'static_library',
       'sources': [
         '<@(schema_files)',
       ],
       # TODO(jschuh): http://crbug.com/167187 size_t -> int
       'msvs_disabled_warnings': [ 4267 ],
       'includes': [
         '../../../../build/json_schema_bundle_compile.gypi',
         '../../../../build/json_schema_compile.gypi',
       ],
       'variables': {
         'chromium_code': 1,
         'non_compiled_schema_files': [
         ],
         # TODO(thestig): Eliminate these on Android. See crbug.com/305852.
         'schema_files': [
           'shell.idl',
         ],
         'cc_dir': 'extensions/shell/common/api',
-        'root_namespace': 'extensions::shell_api',
+        'root_namespace': 'extensions::shell_api::%(namespace)s',
         'impl_dir': 'extensions/shell/browser/api',
       },
       'dependencies': [
         '<(DEPTH)/skia/skia.gyp:skia',
       ],
     },
   ],
 }