Add a Telemetry based cold startup test.

tools/perf/measurements/startup.py

Index: tools/perf/measurements/startup.py
diff --git a/tools/perf/measurements/startup_warm.py b/tools/perf/measurements/startup.py
similarity index 58%
rename from tools/perf/measurements/startup_warm.py
rename to tools/perf/measurements/startup.py
index 7c346b5c50e2d34323210a7dc3b14410f25b1fe0..484b5fdae0d2e6146d9a623a95de2b8fe415229f 100644
--- a/tools/perf/measurements/startup_warm.py
+++ b/tools/perf/measurements/startup.py
@@ -6,9 +6,15 @@ import json
 
 from telemetry.page import page_measurement
 
+class Startup(page_measurement.PageMeasurement):
+  """Performs a measurement of Chromium's startup performance.
+
+  This test must be invoked with either --warm or --cold on the command line. A
+  cold start means none of the Chromium files are in the disk cache. A warm
+  start assumes the OS has already cached much of Chromium's content. For warm
+  tests, you should repeat the page set to ensure it's cached.
+  """
 
-class StartupWarm(page_measurement.PageMeasurement):
-  """Test how long Chrome takes to load when warm."""
   HISTOGRAMS_TO_RECORD = {
     'messageloop_start_time' :
         'Startup.BrowserMessageLoopStartTimeFromMainEntry',
@@ -16,10 +22,27 @@ class StartupWarm(page_measurement.PageMeasurement):
     'open_tabs_time' : 'Startup.BrowserOpenTabs'}
 
   def __init__(self):
-    super(StartupWarm, self).__init__(needs_browser_restart_after_each_run=True,
-                                      discard_first_result=True)
+    super(Startup, self).__init__(needs_browser_restart_after_each_run=True)
+    self._cold = False
+
+  def AddCommandLineOptions(self, parser):
+    parser.add_option('--cold', action='store_true',
+                      help='Clear the OS disk cache before performing the test')
+    parser.add_option('--warm', action='store_true',
+                      help='Start up with everything already cached')
 
   def CustomizeBrowserOptions(self, options):
+    # TODO: Once the bots start running benchmarks, enforce that either --warm
+    # or --cold is explicitly specified.
+    # assert options.warm != options.cold, \
+    #     "You must specify either --warm or --cold"
+    self._cold = options.cold
+
+    if self._cold:
+      options.clear_sytem_cache_for_browser_and_profile_on_start = True
+    else:
+      self.discard_first_result = True
+
     options.AppendExtraBrowserArg('--enable-stats-collection-bindings')
 
     # Old commandline flags used for reference builds.
@@ -35,7 +58,6 @@ class StartupWarm(page_measurement.PageMeasurement):
         'statsCollectionController :'
         'domAutomationController).getBrowserHistogram("%s")')
 
-
     for display_name, histogram_name in self.HISTOGRAMS_TO_RECORD.iteritems():
       result = tab.EvaluateJavaScript(get_histogram_js % histogram_name)
       result = json.loads(result)