Add Masonry to key silk cases.

CL for perf try job: https://codereview.chromium.org/1017683004

BUG=466988

Review URL: https://codereview.chromium.org/1018493004

Cr-Commit-Position: refs/heads/master@{#321838}

tools/perf/page_sets/key_silk_cases.py

@@ -711,6 +711,21 @@ class PolymerTopeka(KeySilkCasesPage):
         window.topeka_page_transitions === 6''')
     interaction.End()
 
+class Masonry(KeySilkCasesPage):
+
+  """ Why: Popular layout hack. """
+
+  def __init__(self, page_set, run_no_page_interactions):
+    super(Masonry, self).__init__(
+      url='file://key_silk_cases/masonry.html',
+      page_set=page_set, run_no_page_interactions=run_no_page_interactions)
+
+  def PerformPageInteractions(self, action_runner):
+    interaction = action_runner.BeginInteraction('animation_interaction')
+    action_runner.ExecuteJavaScript('window.brick()')
+    action_runner.WaitForJavaScriptCondition('window.done')
+    interaction.End()
+
 
 class KeySilkCasesPageSet(page_set_module.PageSet):
 
@@ -755,6 +770,7 @@ class KeySilkCasesPageSet(page_set_module.PageSet):
     self.AddUserStory(UpdateHistoryState(self, run_no_page_interactions))
     self.AddUserStory(SilkFinance(self, run_no_page_interactions))
     self.AddUserStory(PolymerTopeka(self, run_no_page_interactions))
+    self.AddUserStory(Masonry(self, run_no_page_interactions))
 
     for page in self:
       assert (page.__class__.RunPageInteractions ==