Disable smoothness.tough_animation_cases stories on android/mac.

TBR=rnephew@chromium.org

Bug: 755556
Change-Id: Ia1254a8a274961b706b5af71945dc4a7dfc7ac5c
Reviewed-on: https://chromium-review.googlesource.com/614792
Reviewed-by: Simon Hatch <simonhatch@chromium.org>
Reviewed-by: rnephew <rnephew@chromium.org>
Commit-Queue: Simon Hatch <simonhatch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#494459}

tools/perf/benchmarks/smoothness.py

@@ -255,6 +255,19 @@ class StoryExpectations(story_module.expectations.StoryExpectations):
       def SetExpectations(self):
         self.DisableStory('robohornetpro', [story_module.expectations.ALL],
                           'crbug.com/350692')
+        self.DisableStory(
+            'balls_css_keyframe_animations_composited_transform.html',
+            [story_module.expectations.ALL_MOBILE],
+            'crbug.com/755556')
+        self.DisableStory(
+            'mix_blend_mode_animation_difference.html',
+            [story_module.expectations.ALL_MAC],
+            'crbug.com/755556')
+        self.DisableStory(
+            'mix_blend_mode_animation_hue.html',
+            [story_module.expectations.ALL_MAC],
+            'crbug.com/755556')
+
     return StoryExpectations()