Make dart recipes explicitly set GIT_MODE

scripts/slave/recipes/dart/dart.py

 # Copyright 2015 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.
 
 from recipe_engine.recipe_api import Property
 
 DEPS = [
   'depot_tools/bot_update',
   'file',
   'depot_tools/gclient',
   'recipe_engine/path',
   'recipe_engine/platform',
   'recipe_engine/properties',
   'recipe_engine/python',
   'recipe_engine/step',
   'test_utils',
 ]
 
 def RunSteps(api):
   buildername = str(api.properties.get('buildername')) # Convert from unicode.
 
-  api.gclient.set_config('dart')
+  api.gclient.set_config('dart', GIT_MODE=True)
 
   if 'vm-precomp-android' in buildername:
     api.gclient.apply_config('android')
 
   api.bot_update.ensure_checkout(force=True)
   api.gclient.runhooks()
 
   extra_build_args = api.properties.get('build_args', [])
   mode = api.properties.get('mode', 'release')
   target_arch = api.properties.get('target_arch', 'x64')
@@ skipping 32 matching lines @@
       api.properties.generic(mastername='client.dart.FYI',
                              buildername='vm-precomp-android-release',
                              target_arch='arm',
                              build_args=['--os=android'],
                              build_targets=['runtime_precompiled'],
                              test_args=[
                                  '-cprecompiler',
                                  '-rdart_precompiled',
                                  '--exclude-suite=pkg',
                                  '--system=android']))