[Telemetry] Test for display tracing

tools/telemetry/telemetry/internal/platform/android_platform_backend.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 logging
 import os
 import re
 import shutil
 import stat
 import subprocess
@@ skipping 210 matching lines @@
     # Clear any leftover data from previous timed out tests
     self._raw_display_frame_rate_measurements = []
     self._surface_stats_collector = \
         surface_stats_collector.SurfaceStatsCollector(self._device)
     self._surface_stats_collector.Start()
 
   def StopDisplayTracing(self):
     if not self._surface_stats_collector:
       return
 
-    refresh_period, timestamps = self._surface_stats_collector.Stop()
-    pid = self._surface_stats_collector.GetSurfaceFlingerPid()
-    self._surface_stats_collector = None
+    try:
+      refresh_period, timestamps = self._surface_stats_collector.Stop()
+      pid = self._surface_stats_collector.GetSurfaceFlingerPid()
+    finally:
+      self._surface_stats_collector = None
     # TODO(sullivan): should this code be inline, or live elsewhere?
     events = []
     for ts in timestamps:
       events.append({
         'cat': 'SurfaceFlinger',
         'name': 'vsync_before',
         'ts': ts,
         'pid': pid,
         'tid': pid,
         'args': {'data': {
@@ skipping 606 matching lines @@
   for process in psutil.process_iter():
     try:
       if psutil.version_info >= (2, 0):
         if 'adb' in process.name():
           process.cpu_affinity([0])
       else:
         if 'adb' in process.name:
           process.set_cpu_affinity([0])
     except (psutil.NoSuchProcess, psutil.AccessDenied):
       logging.warn('Failed to set adb process CPU affinity')