More polish in prep for CrOS support

tools/gpu/gpu_tools/scrolling_benchmark.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 os
 
 import multi_page_benchmark
 import util
 import chrome_remote_control
 
 class DidNotScrollException(multi_page_benchmark.MeasurementFailure):
@@ skipping 11 matching lines @@
     float(num_frames_sent_to_screen))
 
   return {
       "mean_frame_time_ms": util.RoundTo3DecimalPlaces(
           mean_frame_time_seconds * 1000),
       "dropped_percent": util.RoundTo1DecimalPlace(
          dropped_percent * 100)
       }
 
 class ScrollingBenchmark(multi_page_benchmark.MultiPageBenchmark):
+  def __init__(self):
+    super(ScrollingBenchmark, self).__init__()
+    self.use_gpu_bencharking_extension = True
+
   def ScrollPageFully(self, tab):
     scroll_js_path = os.path.join(os.path.dirname(__file__), 'scroll.js')
     scroll_js = open(scroll_js_path, 'r').read()
 
     # Run scroll test.
     tab.runtime.Execute(scroll_js)
     tab.runtime.Execute("""
       window.__scrollTestResult = null;
       new __ScrollTest(function(rendering_stats) {
         window.__scrollTestResult = rendering_stats;
       });
     """)
 
     # Poll for scroll benchmark completion.
     chrome_remote_control.WaitFor(
         lambda: tab.runtime.Evaluate('window.__scrollTestResult'), 60)
 
     rendering_stats = tab.runtime.Evaluate('window.__scrollTestResult')
 
-    if rendering_stats["numFramesSentToScreen"] == 0:
-      raise scrolling_benchmark.DidNotScrollException()
+    if not (rendering_stats["numFramesSentToScreen"] > 0):
+      raise DidNotScrollException()
     return rendering_stats
 
   def CustomizeBrowserOptions(self, options):
-    options.extra_browser_args.append('--enable-gpu-benchmarking')
+    if self.use_gpu_bencharking_extension:
+      options.extra_browser_args.append('--enable-gpu-benchmarking')
 
   def MeasurePage(self, page, tab):
     rendering_stats = self.ScrollPageFully(tab)
     return _CalcScrollResults(rendering_stats)
 
 
 def Main():
   return multi_page_benchmark.Main(ScrollingBenchmark())