Enable some profile_chrome unit tests on Trybots

systrace/profile_chrome/chrome_startup_tracing_agent_unittest.py

 # Copyright 2015 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 json
 
 from profile_chrome import chrome_startup_tracing_agent
 from profile_chrome import agents_unittest
+from systrace import decorators
 
 
 class ChromeAgentTest(agents_unittest.BaseAgentTest):
+  # TODO: This test seems to fail on the version of Android currently on the
+  # Trybot servers (KTU84P), although it works on Android M. Either upgrade the
+  # version of Android on the Trybot servers or determine if there is a way to
+  # run this agent on Android KTU84P.
+  @decorators.Disabled
   def testTracing(self):
     agent = chrome_startup_tracing_agent.ChromeStartupTracingAgent(
         self.device, self.package_info, False, 'https://www.google.com')
 
     try:
       agent.StartAgentTracing(None)
     finally:
       agent.StopAgentTracing()
 
     result = agent.GetResults()
     json.loads(result.raw_data)