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

tools/perf/page_sets/idle_platform.py

Index: tools/perf/page_sets/idle_platform.py
diff --git a/tools/perf/page_sets/idle_platform.py b/tools/perf/page_sets/idle_platform.py
index b6fffd48a0cb0e930fca9f3439e9bf48202aa75c..b25af546ad7c677209cd9561a4cb25a19406ae09 100644
--- a/tools/perf/page_sets/idle_platform.py
+++ b/tools/perf/page_sets/idle_platform.py
@@ -28,10 +28,19 @@ class _IdleStory(story.Story):
     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):