Android: uses at least 3 samples for surface stats.

build/android/pylib/surface_stats_collector.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 Queue
 import datetime
 import logging
 import re
 import threading
 
@@ skipping 101 matching lines @@
             'vsyncs'),
         SurfaceStatsCollector.Result(
             'frame_lengths' + result_suffix, normalized_frame_lengths,
             'vsyncs'),
     ]
 
   @staticmethod
   def _CalculateBuckets(refresh_period, timestamps):
     results = []
     for pct in [0.99, 0.5]:
-      sliced = timestamps[int(-pct * len(timestamps)) + 3 : ]
+      sliced = timestamps[min(int(-pct * len(timestamps)), -3) : ]
       results += SurfaceStatsCollector._CalculateResults(
           refresh_period, sliced, '_' + str(int(pct * 100)))
     return results
 
   def _StorePerfResults(self):
     if self._use_legacy_method:
       surface_after = self._GetSurfaceStatsLegacy()
       td = surface_after['timestamp'] - self._surface_before['timestamp']
       seconds = td.seconds + td.microseconds / 1e6
       frame_count = (surface_after['page_flip_count'] -
@@ skipping 155 matching lines @@
       try:
         cur_surface = int(match.group(1), 16)
       except Exception:
         logging.error('Failed to parse current surface from ' + match.group(1))
     else:
       logging.warning('Failed to call SurfaceFlinger surface ' + results[0])
     return {
         'page_flip_count': cur_surface,
         'timestamp': datetime.datetime.now(),
     }