Revert of Revert of Change PageTest.WillStartBrowser to depend on platform instead of browser object as it would not ha…

tools/perf/measurements/page_cycler_unittest.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.
 
 import unittest
 
 from telemetry.core import browser_options
 from telemetry.page import page_runner
 from telemetry.results import page_test_results
 from telemetry.unittest import simple_mock
@@ skipping 91 matching lines @@
 
       mock_memory_module = simple_mock.MockObject()
       mock_memory_module.ExpectCall(
         'MemoryMetric').WithArgs(simple_mock.DONT_CARE).WillReturn(
         mock_memory_metric)
 
       real_memory_module = page_cycler.memory
       try:
         page_cycler.memory = mock_memory_module
         browser = FakeBrowser()
-        cycler.WillStartBrowser(browser)
+        cycler.WillStartBrowser(options.browser_options.platform)
         cycler.DidStartBrowser(browser)
       finally:
         page_cycler.memory = real_memory_module
 
     return cycler
 
   def testOptionsColdLoadNoArgs(self):
     cycler = self.SetUpCycler([])
 
     self.assertEquals(cycler._cold_run_start_index, 5)
@@ skipping 83 matching lines @@
         self.assertEqual(values[0].name, '%s.page_load_time' % chart_name)
         self.assertEqual(values[0].units, 'ms')
 
         for value, expected in zip(values[1:], ['gpu', 'renderer', 'browser']):
           self.assertEqual(value.page, page)
           self.assertEqual(value.name,
                            'cpu_utilization.cpu_utilization_%s' % expected)
           self.assertEqual(value.units, '%')
 
         cycler.DidNavigateToPage(page, tab)