Add support for repeated keys in TaskRequest.

appengine/swarming/server/task_result_test.py

Index: appengine/swarming/server/task_result_test.py
diff --git a/appengine/swarming/server/task_result_test.py b/appengine/swarming/server/task_result_test.py
index a1c476adb0b0bcb886d82a3c45c3db71a346bcd8..77c80da2b22ffad4da8bc00d900393c525315df2 100755
--- a/appengine/swarming/server/task_result_test.py
+++ b/appengine/swarming/server/task_result_test.py
@@ -35,13 +35,12 @@ def _gen_request(properties=None, **kwargs):
   """Creates a TaskRequest."""
   props = {
     'command': [u'command1'],
-    'dimensions': {u'pool': u'default'},
+    'dimensions_flat': [u'pool:default'],
     'env': {},
     'execution_timeout_secs': 24*60*60,
     'io_timeout_secs': None,
   }
   props.update(properties or {})
-  props['dimensions_dict'] = props.pop('dimensions')
   now = utils.utcnow()
   args = {
     'created_ts': now,