Rename startup_tests.py Telemetry test to startup_benchmark.py

tools/perf/perf_tools/startup_benchmark.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.
 
 from telemetry.page import page_benchmark
 
 # Test how long Chrome takes to load when warm.
 class PerfWarm(page_benchmark.PageBenchmark):
   def __init__(self):
     super(PerfWarm, self).__init__(needs_browser_restart_after_each_run=True,
                                    discard_first_result=True)
 
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArg('--dom-automation')
     options.AppendExtraBrowserArg('--reduce-security-for-dom-automation-tests')
 
   def MeasurePage(self, page, tab, results):
     result = tab.EvaluateJavaScript("""
       domAutomationController.getBrowserHistogram(
           "Startup.BrowserMessageLoopStartTimeFromMainEntry")
       """)
     results.Add('startup_time', 'ms', result)