Modifies the constructor for idle test.

The idle page test runs with and without MR extension, but there is no good way to distinguish them because they use the same name.
Now, for the test with no MR extension, we use #no_media_router to identify it.

Change-Id: Iac6bc9f1ab411e14c0d51129290c293394f8ded9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1772569
Commit-Queue: Clifford Cheng <cliffordcheng@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690823}

tools/perf/contrib/media_router_benchmarks/media_router_pages.py

@@ -27,12 +27,12 @@ class SharedState(shared_page_state.SharedPageState):
 class CastIdlePage(MediaRouterBasePage):
   """Cast page to open a cast-enabled page and do nothing."""
 
-  def __init__(self, page_set):
+  def __init__(self, page_set, name='basic_test.html'):
     super(CastIdlePage, self).__init__(
         page_set=page_set,
         url='file://test_site/basic_test.html',
         shared_page_state_class=SharedState,
-        name='basic_test.html')
+        name=name)
 
   def RunPageInteractions(self, action_runner):
     # Wait for 5s after Chrome is opened in order to get consistent results.
@@ -160,4 +160,4 @@ class CPUMemoryPageSet(story.StorySet):
   def __init__(self):
     super(CPUMemoryPageSet, self).__init__(
         cloud_storage_bucket=story.PARTNER_BUCKET)
-    self.AddStory(CastIdlePage(self))
+    self.AddStory(CastIdlePage(self, 'basic_test.html#no_component_extension'))