Skips testActivateTab on old browsers which don't support tab control.

tools/telemetry/telemetry/tab_unittest.py

 # Copyright (c) 2012 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 telemetry import tab_test_case
 from telemetry import tab_crash_exception
 from telemetry import util
 
 
 def _IsDocumentVisible(tab):
   state = tab.runtime.Evaluate('document.webkitVisibilityState')
@@ skipping 12 matching lines @@
 
   def testTabBrowserIsRightBrowser(self):
     self.assertEquals(self._tab.browser, self._browser)
 
   def testRendererCrash(self):
     self.assertRaises(tab_crash_exception.TabCrashException,
                       lambda: self._tab.page.Navigate('chrome://crash',
                                                       timeout=5))
 
   def testActivateTab(self):
+    if not self._browser.supports_tab_control:
+      return
     self.assertTrue(_IsDocumentVisible(self._tab))
     new_tab = self._browser.tabs.New()
     util.WaitFor(lambda: _IsDocumentVisible(new_tab), timeout=5)
     self.assertFalse(_IsDocumentVisible(self._tab))
     self._tab.Activate()
     util.WaitFor(lambda: _IsDocumentVisible(self._tab), timeout=5)
     self.assertFalse(_IsDocumentVisible(new_tab))