[Telemetry] Disable spaceport and tough_canvas_cases on mac.

tools/perf/benchmarks/smoothness.py

 # Copyright (c) 2013 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
+
+import sys
+
 from telemetry import test
 
 from measurements import smoothness
 
 
 class SmoothnessTop25(test.Test):
   """Measures rendering statistics while scrolling down the top 25 web pages.
 
   http://www.chromium.org/developers/design-documents/rendering-benchmarks"""
   test = smoothness.Smoothness
   page_set = 'page_sets/top_25.json'
 
 
 class SmoothnessToughCanvasCases(test.Test):
   test = smoothness.Smoothness
+  enabled = sys.platform != 'darwin'
   page_set = 'page_sets/tough_canvas_cases.json'
 
 
 class SmoothnessKeyMobileSites(test.Test):
   """Measures rendering statistics while scrolling down the key mobile sites.
 
   http://www.chromium.org/developers/design-documents/rendering-benchmarks"""
   test = smoothness.Smoothness
   page_set = 'page_sets/key_mobile_sites.json'