For page cyclers, move power metrics start to WillNavigate.

tools/perf/measurements/page_cycler.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.
 
 """The page cycler measurement.
 
 This measurement registers a window load handler in which is forces a layout and
 then records the value of performance.now(). This call to now() measures the
 time from navigationStart (immediately after the previous page's beforeunload
 event) until after the layout in the page's load event. In addition, two garbage
@@ skipping 64 matching lines @@
     # page cyclers which use the filesystem.
     tab.Navigate(tab.browser.http_server.UrlOf('nonexistent.html'))
 
   def WillNavigateToPage(self, page, tab):
     page.script_to_evaluate_on_commit = self._page_cycler_js
     if self.ShouldRunCold(page.url):
       tab.ClearCache(force=True)
     if self._report_speed_index:
       self._speedindex_metric.Start(page, tab)
     self._cpu_metric.Start(page, tab)
+    self._power_metric.Start(page, tab)
 
   def DidNavigateToPage(self, page, tab):
     self._memory_metric.Start(page, tab)
-    self._power_metric.Start(page, tab)
     if self._record_v8_object_stats:
       self._v8_object_stats_metric.Start(page, tab)
 
   def CustomizeBrowserOptions(self, options):
     memory.MemoryMetric.CustomizeBrowserOptions(options)
     power.PowerMetric.CustomizeBrowserOptions(options)
     iometric.IOMetric.CustomizeBrowserOptions(options)
     options.AppendExtraBrowserArgs('--js-flags=--expose_gc')
 
     if self._record_v8_object_stats:
@@ skipping 65 matching lines @@
     # preserve any initial profile cache for as long as possible.
     # The second is that, if we did cold runs first, we'd have a transition
     # page set during which we wanted the run for each URL to both
     # contribute to the cold data and warm the catch for the following
     # warm run, and clearing the cache before the load of the following
     # URL would eliminate the intended warmup for the previous URL.
     return (self._has_loaded_page[url] >= self._cold_run_start_index)
 
   def results_are_the_same_on_every_page(self):
     return False