Refactor all video related processing to its own class

tools/perf/metrics/speedindex.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 collections
 
 from metrics import Metric
 from telemetry.core import bitmap
 
 
@@ skipping 120 matching lines @@
     # TODO(tonyg): Bitrate is arbitrary here. Experiment with screen capture
     # overhead vs. speed index accuracy and set the bitrate appropriately.
     tab.StartVideoCapture(min_bitrate_mbps=4)
 
   def Stop(self, tab):
     # Ignore white because Chrome may blank out the page during load and we want
     # that to count as 0% complete. Relying on this fact, we also blank out the
     # previous page to white. The tolerance of 8 experimentally does well with
     # video capture at 4mbps. We should keep this as low as possible with
     # supported video compression settings.
+    video_capture = tab.StopVideoCapture()
     histograms = [(time, bmp.ColorHistogram(ignore_color=bitmap.WHITE,
                                             tolerance=8))
-                  for time, bmp in tab.StopVideoCapture()]
+                  for time, bmp in video_capture.GetVideoFrameIter()]
 
     start_histogram = histograms[0][1]
     final_histogram = histograms[-1][1]
     total_distance = start_histogram.Distance(final_histogram)
 
     def FrameProgress(histogram):
       if total_distance == 0:
         if histogram.Distance(final_histogram) == 0:
           return 1.0
         else:
@@ skipping 141 matching lines @@
     frame = paint_event.args['frameId']
     return (frame,) + GetBox(paint_event.args['data']['clip'])
 
   def _GroupEventByRectangle(self, paint_events):
     """Group all paint events according to the rectangle that they update."""
     result = collections.defaultdict(list)
     for event in paint_events:
       assert event.name == 'Paint'
       result[self._GetRectangle(event)].append(event)
     return result