[Telemetry] Fix idle platform story so that it has a url.

tools/perf/page_sets/idle_platform.py

 # Copyright 2017 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.
 import time
 
 from telemetry.page import shared_page_state
 from telemetry import story
 
 
 class _IdleSharedState(shared_page_state.SharedPageState):
@@ skipping 10 matching lines @@
 
   def DidRunStory(self, _):
     self._current_story = None
 
 
 class _IdleStory(story.Story):
   def __init__(self, name, duration):
     super(_IdleStory, self).__init__(
         shared_state_class=_IdleSharedState, name=name)
     self._duration = duration
+    # https://github.com/catapult-project/catapult/issues/3489
+    # Even though there is no actual url being used, it is required for
+    # uploading results using the --upload-results flag. Remove url when
+    # it is no longer needed.
+    self._url = name
 
   def Run(self, shared_state):
     time.sleep(self._duration)
 
+  @property
+  def url(self):
+    return self._url
+
 
 class IdleStorySet(story.StorySet):
   def __init__(self):
     super(IdleStorySet, self).__init__()
     self.AddStory(_IdleStory('IdleStory_10s', 10))
     self.AddStory(_IdleStory('IdleStory_60s', 60))
     self.AddStory(_IdleStory('IdleStory_120s', 120))