Allow defining custom navigation on a per-page basis.

tools/perf/measurements/tab_switching.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.
 
 """The tab switching measurement.
 
 This measurement opens pages in different tabs. After all the tabs have opened,
 it cycles through each tab in sequence, and records a histogram of the time
 between when a tab was first requested to be shown, and when it was painted.
 """
@@ skipping 12 matching lines @@
 
   def CanRunForPage(self, page):
     return not page.page_set.pages.index(page)
 
   def DidNavigateToPage(self, page, tab):
     for i in xrange(1, len(page.page_set.pages)):
       t = tab.browser.tabs.New()
 
       page_state = page_runner.PageState()
       page_state.PreparePage(page.page_set.pages[i], t)
+      page_state.ImplicitPageNavigation(page.page_set.pages[i], t)
 
   def MeasurePage(self, _, tab, results):
     """Although this is called MeasurePage, we're actually using this function
     to cycle through each tab that was opened via DidNavigateToPage and
     thenrecord a single histogram for the tab switching metric.
     """
     histogram_name = 'MPArch.RWH_TabSwitchPaintDuration'
     histogram_type = 'getBrowserHistogram'
     first_histogram = histogram_util.GetHistogramFromDomAutomation(
         histogram_type, histogram_name, tab)
@@ skipping 12 matching lines @@
       prev_histogram = histogram_util.GetHistogramFromDomAutomation(
           histogram_type, histogram_name, tab)
 
     last_histogram = histogram_util.GetHistogramFromDomAutomation(
         histogram_type, histogram_name, tab)
     diff_histogram = histogram_util.SubtractHistogram(last_histogram,
         first_histogram)
 
     results.AddSummary(histogram_name, '', diff_histogram,
         data_type='unimportant-histogram')