Android: uses at least 3 samples for surface stats.

Follow-up on crrev.com/204593, fixes the bucket calculation.

BUG=

Review URL: https://chromiumcodereview.appspot.com/19055003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@211196 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/pylib/surface_stats_collector.py

@@ -119,7 +119,7 @@ class SurfaceStatsCollector(object):
   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