[perf] Disable tab_switching.top_10 on mac-reference

tools/perf/benchmarks/tab_switching.py

 # Copyright 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.
 
 from core import perf_benchmark
 
 from measurements import tab_switching
 import page_sets
 from telemetry import benchmark
 
 
 @benchmark.Enabled('has tabs')
 @benchmark.Disabled('android')  # http://crbug.com/460084
+@benchmark.Disabled('mac-reference')  # http://crbug.com/634378
 class TabSwitchingTop10(perf_benchmark.PerfBenchmark):
   """This test records the MPArch.RWH_TabSwitchPaintDuration histogram.
 
   The histogram is a measure of the time between when a tab was requested to be
   shown, and when first paint occurred. The script opens 10 pages in different
   tabs, waits for them to load, and then switches to each tab and records the
   metric. The pages were chosen from Alexa top ranking sites.
   """
   test = tab_switching.TabSwitching
   page_set = page_sets.Top10PageSet
@@ skipping 72 matching lines @@
   shown, and when first paint occurred. The script opens each page in different
   tabs, waits for them to load, and then switches to each tab and records the
   metric. The pages were chosen by hand to stress the image decoding system.
   """
   test = tab_switching.TabSwitching
   page_set = page_sets.ToughImageCasesPageSet
 
   @classmethod
   def Name(cls):
     return 'tab_switching.tough_image_cases'