Split bundle generation steps so that API registration is generated in browser, not common.

extensions/shell/browser/api/api_registration.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_registration',
+      'type': 'static_library',
+      # TODO(jschuh): http://crbug.com/167187 size_t -> int
+      'msvs_disabled_warnings': [ 4267 ],
+      'includes': [
+        '../../../../build/json_schema_bundle_registration_compile.gypi',
+        '../../common/api/schemas.gypi',
+      ],
+    },
+  ],
+}