Update fetch to support more flexible refspecs

recipes/chromium.py

Index: recipes/chromium.py
diff --git a/recipes/chromium.py b/recipes/chromium.py
index 7ebf9841ae5797be80b6ef9930c2b5c28c2dc167..6416ee0bbd7a4b1240e7a04acd2132a018906499 100644
--- a/recipes/chromium.py
+++ b/recipes/chromium.py
@@ -31,11 +31,9 @@ class Chromium(recipe_util.Recipe):
       spec['target_os'] = props['target_os'].split(',')
     if props.get('target_os_only'):
       spec['target_os_only'] = props['target_os_only']
-    checkout_type = 'gclient_git'
-    spec_type = '%s_spec' % checkout_type
     return {
-      'type': checkout_type,
-      spec_type: spec,
+      'type': 'gclient_git',
+      'gclient_git_spec': spec,
     }
 
   @staticmethod