[tools/perf] Delete unused variable

tools/perf/benchmarks/blink_perf.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.
 
 import os
 
 from core import path_util
 from core import perf_benchmark
 
 from telemetry import benchmark
@@ skipping 63 matching lines @@
 class _BlinkPerfMeasurement(page_test.PageTest):
   """Tuns a blink performance test and reports the results."""
 
   def __init__(self):
     super(_BlinkPerfMeasurement, self).__init__()
     with open(os.path.join(os.path.dirname(__file__),
                            'blink_perf.js'), 'r') as f:
       self._blink_perf_js = f.read()
 
   def WillNavigateToPage(self, page, tab):
+    del tab  # unused
     page.script_to_evaluate_on_commit = self._blink_perf_js
 
   def CustomizeBrowserOptions(self, options):
     options.AppendExtraBrowserArgs([
         '--js-flags=--expose_gc',
         '--enable-experimental-web-platform-features',
         '--disable-gesture-requirement-for-media-playback',
         '--enable-experimental-canvas-features',
         # TODO(qinmin): After fixing crbug.com/592017, remove this command line.
         '--reduce-security-for-testing'
@@ skipping 239 matching lines @@
 
   def CreateStorySet(self, options):
     path = os.path.join(BLINK_PERF_BASE_DIR, 'Pywebsocket')
     return CreateStorySetFromPath(
         path, SKIPPED_FILE,
         shared_page_state_class=_SharedPywebsocketPageState)
 
   @classmethod
   def ShouldDisable(cls, possible_browser):
     return cls.IsSvelte(possible_browser)  # http://crbug.com/551950