[tools/perf] Delete unused variable

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.
 Power usage is also measured.
@@ skipping 30 matching lines @@
     ])
     # Enable background networking so we can test its impact on power usage.
     options.disable_background_networking = False
     power.PowerMetric.CustomizeBrowserOptions(options)
 
   def WillStartBrowser(self, platform):
     self.first_page_in_storyset = True
     self._power_metric = power.PowerMetric(platform, TabSwitching.SAMPLE_TIME)
 
   def TabForPage(self, page, browser):
+    del page  # unused
     if self.first_page_in_storyset:
       # The initial browser window contains a single tab, navigate that tab
       # rather than creating a new one.
       self.first_page_in_storyset = False
       return browser.tabs[0]
 
     return browser.tabs.New()
 
   def StopBrowserAfterPage(self, browser, page):
     # Restart the browser after the last page in the pageset.
@@ skipping 40 matching lines @@
                                                       first_histogram)
 
     results.AddSummaryValue(
         histogram.HistogramValue(None, display_name, 'ms',
                                  raw_value_json=diff_histogram,
                                  important=False))
 
     keychain_metric.KeychainMetric().AddResults(tab, results)
 
   def DidRunPage(self, platform):
+    del platform  # unused
     self._power_metric.Close()