Extensions: Do not depend on device_serial_mojo target when extensions are turned off.

extensions/extensions.gyp

 # Copyright 2013 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.
 
 {
   'variables': {
     'chromium_code': 1,
   },
   'targets': [
     {
       # GN version: //extensions/common
       'target_name': 'extensions_common',
       'type': 'static_library',
       'dependencies': [
         # TODO(benwells): figure out what to do with the api target and
         # api resources compiled into the chrome resource bundle.
         # http://crbug.com/162530
         '../chrome/chrome_resources.gyp:chrome_resources',
         '../components/components.gyp:url_matcher',
         '../content/content.gyp:content_common',
         '../crypto/crypto.gyp:crypto',
-        # For Mojo generated headers for generated_api.cc.
-        '../device/serial/serial.gyp:device_serial_mojo',
         '../ipc/ipc.gyp:ipc',
         '../net/net.gyp:net',
         '../third_party/re2/re2.gyp:re2',
         '../ui/base/ui_base.gyp:ui_base',
         '../ui/gfx/gfx.gyp:gfx_geometry',
         '../ui/gfx/ipc/gfx_ipc.gyp:gfx_ipc',
         '../url/url.gyp:url_lib',
         '../third_party/libxml/libxml.gyp:libxml',
         'common/api/api.gyp:extensions_api',
         'extensions_strings.gyp:extensions_strings',
@@ skipping 176 matching lines @@
         'common/value_counter.cc',
         'common/value_counter.h',
         'common/view_type.cc',
         'common/view_type.h',
       ],
       # Disable c4267 warnings until we fix size_t to int truncations.
       'msvs_disabled_warnings': [ 4267, ],
       'conditions': [
         ['enable_extensions==1', {
           'dependencies': [
+            # For Mojo generated headers for generated_api.cc.
+            '../device/serial/serial.gyp:device_serial_mojo',
             '../device/usb/usb.gyp:device_usb',
           ],
           'sources!': [
             'common/extension_api_stub.cc',
           ],
         }, {  # enable_extensions == 0
           'sources!': [
             'common/api/messaging/message.h',
             'common/api/sockets/sockets_manifest_data.cc',
             'common/api/sockets/sockets_manifest_data.h',
@@ skipping 685 matching lines @@
           'browser/api/cast_channel/logging.proto'
       ],
       'variables': {
           'proto_in_dir': 'browser/api/cast_channel',
           'proto_out_dir': 'extensions/browser/api/cast_channel',
       },
       'includes': [ '../build/protoc.gypi' ]
     },
   ]
 }