Make chromium_tests recipe module explicitly set GIT_MODE

scripts/slave/recipes/chromium.expected/full_client_skia_Linux_Tests_Trybot.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "\nimport sys, os\npath = sys.argv[1]\nmode = int(sys.argv[2])\nif not os.path.isdir(path):\n  if os.path.exists(path):\n    print \"%s exists but is not a dir\" % path\n    sys.exit(1)\n  os.makedirs(path, mode)\n",
       "[BUILDER_CACHE]/Linux_Tests_Trybot",
       "511"
     ],
     "name": "makedirs checkout path",
@@ skipping 15 matching lines @@
       "python",
       "-u",
       "RECIPE_MODULE[depot_tools::bot_update]/resources/bot_update.py",
       "--master",
       "client.skia",
       "--builder",
       "Linux Tests-Trybot",
       "--slave",
       "TestSlavename",
       "--spec",
-      "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'svn://svn-mirror.golo.chromium.org/blink/trunk'}, 'deps_file': 'DEPS', 'managed': True, 'name': 'src', 'url': 'svn://svn-mirror.golo.chromium.org/chrome/trunk/src'}]",
+      "cache_dir = '[GIT_CACHE]'\nsolutions = [{'custom_vars': {'googlecode_url': 'svn://svn-mirror.golo.chromium.org/%s', 'nacl_trunk': 'svn://svn-mirror.golo.chromium.org/native_client/trunk', 'sourceforge_url': 'svn://svn-mirror.golo.chromium.org/%(repo)s', 'webkit_trunk': 'https://chromium.googlesource.com/chromium/blink.git'}, 'deps_file': '.DEPS.git', 'managed': True, 'name': 'src', 'url': 'https://chromium.googlesource.com/chromium/src.git'}]",
       "--root",
       "src/third_party/skia",
       "--revision_mapping_file",
       "{\"src\": \"got_chromium_revision\", \"src/buildtools\": \"got_buildtools_revision\", \"src/native_client\": \"got_nacl_revision\", \"src/third_party/angle\": \"got_angle_revision\", \"src/third_party/skia\": \"got_revision\", \"src/third_party/webrtc\": \"got_webrtc_revision\", \"src/tools/swarming_client\": \"got_swarming_client_revision\", \"src/v8\": \"got_v8_revision\"}",
       "--git-cache-dir",
       "[GIT_CACHE]",
       "--output_json",
       "/path/to/tmp/json",
       "--revision",
       "src@HEAD",
@@ skipping 443 matching lines @@
       "GOMA_SERVICE_ACCOUNT_JSON_FILE": "/creds/service_accounts/service-account-goma-client.json"
     },
     "name": "Upload to test-results [browser_tests on Ubuntu-12.04]"
   },
   {
     "name": "$result",
     "recipe_result": null,
     "status_code": 0
   }
 ]