telemetry: Disable smoothness.key_silk_cases page using expectations.

key_silk_cases.Page26 was disabled by manually removing it from the
StorySet. This is probably a relic of a time before story expectations
were implemented. This CL disables the page using expectations.

BUG=461127

Change-Id: I055b6bd78667a16b59120211698dd0281419e25e
Reviewed-on: https://chromium-review.googlesource.com/884987Reviewed-by: Ned Nguyen <nednguyen@google.com>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
Cr-Commit-Position: refs/heads/master@{#531873}

tools/perf/benchmarks/smoothness.py

@@ -162,15 +162,6 @@ class SmoothnessKeySilkCases(_Smoothness):
   def Name(cls):
     return 'smoothness.key_silk_cases'
 
-  def CreateStorySet(self, options):
-    stories = super(SmoothnessKeySilkCases, self).CreateStorySet(options)
-    # Page26 (befamous) is too noisy to be useful; crbug.com/461127
-    to_remove = [story for story in stories
-                 if isinstance(story, page_sets.key_silk_cases.Page26)]
-    for story in to_remove:
-      stories.RemoveStory(story)
-    return stories
-
 
 @benchmark.Owner(emails=['vmiura@chromium.org'])
 class SmoothnessGpuRasterizationTop25(_Smoothness):

tools/perf/expectations.config

@@ -132,6 +132,7 @@ crbug.com/756119 [ Android ] smoothness.key_mobile_sites_smooth/http://digg.com
 # Benchmark: smoothness.key_silk_cases
 [ All ] smoothness.key_silk_cases/inbox_app.html?slide_drawer [ Skip ]
 crbug.com/780525 [ All ] smoothness.key_silk_cases/https://polymer-topeka.appspot.com/ [ Skip ]
+crbug.com/461127 [ All ] smoothness.key_silk_cases/http://s.codepen.io/befamous/fullpage/pFsqb?scroll [ Skip ]
 
 # Benchmark: smoothness.maps
 crbug.com/653993 [ Android_Webview ] smoothness.maps/maps_perf_test [ Skip ]