Add perf tests for starting Chrome with URL

tools/telemetry/telemetry/page/page_test.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.
 import logging
 
 from telemetry.page import test_expectations
 from telemetry.page.actions import all_page_actions
 from telemetry.page.actions import interact
 from telemetry.page.actions import navigate
 from telemetry.page.actions import page_action
@@ skipping 89 matching lines @@
   @property
   def close_tabs_before_run(self):
     """When set to True, all tabs are closed before running the test for the
     first time."""
     return self._close_tabs_before_run
 
   @close_tabs_before_run.setter
   def close_tabs_before_run(self, close_tabs):
     self._close_tabs_before_run = close_tabs
 
+  def AlwaysRestartBrowserForEachRun(self):
+    """ Should be browser be restarted after each run - browser independent.

[jeremy, 2013/12/15 13:03:36]

nit: "Should the..."

And if this returns false that means that the browser gets restarted after the
whole pageset?

[aberent, 2013/12/16 17:07:43]

Done.

+
+    Can be called at any time."""
+    return self._needs_browser_restart_after_each_run
+
   def NeedsBrowserRestartAfterEachRun(self, browser):  # pylint: disable=W0613
-    """Override to specify browser restart after each run."""
-    return self._needs_browser_restart_after_each_run
+    """Browser dependent version of AlwaysRestartBrowserForEachRun.
+
+    Can only be called once the browser has stared. Override this if the test
+    has to restart the browser for some browsers but not all."""

[jeremy, 2013/12/15 13:03:36]

Not clear what "browser dependent" means in this context :( Can you please
expand/rephrase the comment?

esp. the difference between this and the previous function.

[aberent, 2013/12/16 17:07:43]

I have renamed this to more accurately reflect what it does, and extended the
comments. The reason for this function is that image_decoding.py needs to call a
browser function to decide whether to restart the browser. 

+    return self.AlwaysRestartBrowserForEachRun()
 
   def AddCommandLineOptions(self, parser):
     """Override to expose command-line options for this test.
 
     The provided parser is an optparse.OptionParser instance and accepts all
     normal results. The parsed options are available in Run as
     self.options."""
     pass
 
   def CustomizeBrowserOptions(self, options):
@@ skipping 146 matching lines @@
 
   def IsExiting(self):
     return self._exit_requested
 
   def RequestExit(self):
     self._exit_requested = True
 
   @property
   def action_name_to_run(self):
     return self._action_name_to_run