Dart: Update the config for the "fetch dart" command.

Bug: https://bugs.chromium.org/p/chromium/issues/detail?id=737149
Change-Id: I72e65056519338039d02246dcdfdb3e71c980b92
Reviewed-on: https://chromium-review.googlesource.com/649608
Reviewed-by: Emma Söderberg <emso@chromium.org>
Reviewed-by: Paweł Hajdan Jr. <phajdan.jr@chromium.org>
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: William Hesse <whesse@google.com>

fetch_configs/dart.py

@@ -14,7 +14,7 @@ class Dart(config_util.Config):
 
   @staticmethod
   def fetch_spec(props):
-    url = 'https://github.com/dart-lang/sdk.git'
+    url = 'https://dart.googlesource.com/sdk.git'
     solution = {
       'name'   :'sdk',
       'url'    : url,