[Telemetry] Make chrome_tracing_agent state more resilient to tracing exception.

Because ChromeTracingAgent class has global states, when any
exception was raised inside StopTracing method, the active tracing
state of this class is not set to False, making subsequent unittest that
try to StartTracing fails because of this.

Long term fix of this depends on crbug.com/317481 be fixed so that
ChromeTracingAgent no longer have global state.

BUG=459807

Review URL: https://codereview.chromium.org/997193002

Cr-Commit-Position: refs/heads/master@{#320799}

tools/telemetry/telemetry/core/platform/tracing_agent/chrome_tracing_agent.py

 # Copyright 2014 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 sys
+import traceback
 
 from telemetry.core.platform import tracing_agent
 
@@ -9,6 +11,10 @@ class ChromeTracingStartedError(Exception):
   pass
 
 
+class ChromeTracingStoppedError(Exception):
+  pass
+
+
 class ChromeTracingAgent(tracing_agent.TracingAgent):
   # A singleton map from platform backends to maps of uniquely-identifying
   # remote port (which may be the same as local port) to DevToolsClientBackend.
@@ -90,9 +96,21 @@ class ChromeTracingAgent(tracing_agent.TracingAgent):
   def Stop(self, trace_data_builder):
     devtools_clients_map = (
       self._platform_backends_to_devtools_clients_maps[self._platform_backend])
-    for _, devtools_client in devtools_clients_map.iteritems():
+    raised_execption_messages = []
+    for devtools_port, devtools_client in devtools_clients_map.iteritems():
       # We do not check for stale DevTools client, so that we get an
       # exception if there is a stale client. This is because we
       # will potentially lose data if there is a stale client.
-      devtools_client.StopChromeTracing(trace_data_builder)
+      try:
+        devtools_client.StopChromeTracing(trace_data_builder)
+      except Exception:
+        raised_execption_messages.append(
+          'Error when trying to stop tracing on devtools at port %s:\n%s'
+          % (devtools_port,
+             ''.join(traceback.format_exception(*sys.exc_info()))))
+
     self._is_active = False
+    if raised_execption_messages:
+      raise ChromeTracingStoppedError(
+          'Exceptions raised when trying to stop devtool tracing\n:' +
+          '\n'.join(raised_execption_messages))

tools/telemetry/telemetry/core/platform/tracing_agent/chrome_tracing_agent_unittest.py

@@ -16,6 +16,7 @@ class FakeDevtoolsClient(object):
     self.is_alive = True
     self.tracing_started = False
     self.remote_port = remote_port
+    self.will_raise_exception_in_stop_tracing = False
 
   def IsAlive(self):
     return self.is_alive
@@ -25,6 +26,8 @@ class FakeDevtoolsClient(object):
 
   def StopChromeTracing(self, _trace_data_builder):
     self.tracing_started = False
+    if self.will_raise_exception_in_stop_tracing:
+      raise Exception
 
   def IsChromeTracingSupported(self):
     return True
@@ -142,3 +145,31 @@ class ChromeTracingAgentUnittest(unittest.TestCase):
     self.assertTrue(devtool4.tracing_started)
     self.StopTracing(tracing_agent2)
     self.assertFalse(devtool4.tracing_started)
+
+  def testExceptionRaisedInStopTracing(self):
+    devtool1 = FakeDevtoolsClient(1)
+    devtool2 = FakeDevtoolsClient(2)
+    # Register devtools 1, 2 on platform 1
+    chrome_tracing_agent.ChromeTracingAgent.RegisterDevToolsClient(
+        devtool1, self.platform1)
+    chrome_tracing_agent.ChromeTracingAgent.RegisterDevToolsClient(
+        devtool2, self.platform1)
+    tracing_agent1 = self.StartTracing(self.platform1)
+
+    self.assertTrue(devtool1.tracing_started)
+    self.assertTrue(devtool2.tracing_started)
+
+    devtool2.will_raise_exception_in_stop_tracing = True
+    with self.assertRaises(chrome_tracing_agent.ChromeTracingStoppedError):
+      self.StopTracing(tracing_agent1)
+
+    devtool1.is_alive = False
+    devtool2.is_alive = False
+    # Register devtools 3 on platform 1 should not raise any exception.
+    devtool3 = FakeDevtoolsClient(3)
+    chrome_tracing_agent.ChromeTracingAgent.RegisterDevToolsClient(
+        devtool3, self.platform1)
+
+    # Start & Stop tracing on platform 1 should work just fine.
+    tracing_agent2 = self.StartTracing(self.platform1)
+    self.StopTracing(tracing_agent2)

tools/telemetry/telemetry/core/platform/tracing_controller_unittest.py

@@ -8,8 +8,7 @@ from telemetry.core.platform import tracing_options
 from telemetry.unittest_util import tab_test_case
 
 class TracingControllerTest(tab_test_case.TabTestCase):
-  # Disabled due to http://crbug.com/459807
-  @decorators.Disabled
+
   @decorators.Isolated
   def testModifiedConsoleTime(self):
     category_filter = tracing_category_filter.TracingCategoryFilter()