Add a mimeHandler extension API.

extensions/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': [
     {
+      # GN version: //extensions/common/api:mojom
+      'target_name': 'extensions_api_mojom',
+      # The type of this target must be none. This is so that resources can
+      # depend upon this target for generating the js bindings files. Any
+      # generated cpp files must be listed explicitly in chrome_api.
+      'type': 'none',
+      'includes': [
+        '../../../mojo/mojom_bindings_generator.gypi',
+      ],
+      'sources': [
+        'mime_handler.mojom',
+      ],
+    },
+    {
       # GN version: //extensions/common/api
       'target_name': 'extensions_api',
       'type': 'static_library',
       # 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',
         'schemas.gypi',
       ],
+      'dependencies': [
+        'extensions_api_mojom',
+      ],
+      'sources': [
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/api/mime_handler.mojom.cc',
+        '<(SHARED_INTERMEDIATE_DIR)/extensions/common/api/mime_handler.mojom.h',
+      ],
     },
     {
       # Protobuf compiler / generator for chrome.cast.channel-related protocol buffers.
       # GN version: //extensions/browser/api/cast_channel:cast_channel_proto
       'target_name': 'cast_channel_proto',
       'type': 'static_library',
       'sources': [
           'cast_channel/authority_keys.proto',
           'cast_channel/cast_channel.proto',
           'cast_channel/logging.proto',
       ],
       'variables': {
           'proto_in_dir': 'cast_channel',
           'proto_out_dir': 'extensions/common/api/cast_channel',
       },
       'includes': [ '../../../build/protoc.gypi' ]
     },
   ],
 }