[Telemetry] Clear tracing state before browser start

telemetry/telemetry/internal/platform/tracing_agent/chrome_tracing_agent.py

 # Copyright 2015 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 atexit
 import logging
 import os
 import shutil
 import stat
 import sys
 import tempfile
 import traceback
 
 from telemetry.internal.platform import tracing_agent
 from telemetry.internal.platform.tracing_agent import (
     chrome_tracing_devtools_manager)
 
 _DESKTOP_OS_NAMES = ['linux', 'mac', 'win']
 _STARTUP_TRACING_OS_NAMES = _DESKTOP_OS_NAMES + ['android']
 
 # The trace config file path should be the same as specified in
 # src/components/tracing/trace_config_file.[h|cc]
 _CHROME_TRACE_CONFIG_DIR_ANDROID = '/data/local/'
 _CHROME_TRACE_CONFIG_FILE_NAME = 'chrome-trace-config.json'
 
 
+def ClearStarupTracingStateIfNeeded(platform_backend):
+  # Trace config file has fixed path on Android and temporary path on desktop.
+  if platform_backend.GetOSName() == 'android':
+    trace_config_file = os.path.join(_CHROME_TRACE_CONFIG_DIR_ANDROID,
+                                     _CHROME_TRACE_CONFIG_FILE_NAME)
+    platform_backend.device.RunShellCommand(
+        ['rm', '-f', trace_config_file], check_return=True, as_root=True)
+
+
 class ChromeTracingStartedError(Exception):
   pass
 
 
 class ChromeTracingStoppedError(Exception):
   pass
 
 
 class ChromeTracingAgent(tracing_agent.TracingAgent):
   def __init__(self, platform_backend):
@@ skipping 166 matching lines @@
     for backend in self._IterInspectorBackends():
       backend.EvaluateJavaScript("console.timeEnd('flush-tracing');")
 
   def _IterInspectorBackends(self):
     for client in chrome_tracing_devtools_manager.GetDevToolsClients(
         self._platform_backend):
       context_map = client.GetUpdatedInspectableContexts()
       for context in context_map.contexts:
         if context['type'] in ['iframe', 'page', 'webview']:
           yield context_map.GetInspectorBackend(context['id'])