Check the context type in StopChromeTracing

DevToolsClientBackend.StopChromeTracing() tries to call console.time & console.timeEnd.
But in ServiceWorker telemetry tests, ServiceWorker may have already stopped by itself.
This is causing the test flakiness.

So this cl add checking if the context type is 'iframe', 'page'  or 'webview'.

BUG=433943
TEST=./tools/perf/run_benchmark --browser-executable=~/chromium/src/out/Debug/chrome --also-run-disabled-tests service_worker.service_worker

Review URL: https://codereview.chromium.org/884573004

Cr-Commit-Position: refs/heads/master@{#317730}

tools/telemetry/telemetry/core/backends/chrome_inspector/devtools_client_backend.py

@@ -134,6 +134,8 @@ class DevToolsClientBackend(object):
   def StopChromeTracing(self, trace_data_builder, timeout=30):
     context_map = self.GetUpdatedInspectableContexts()
     for context in context_map.contexts:
+      if context['type'] not in ['iframe', 'page', 'webview']:
+        continue
       context_id = context['id']
       backend = context_map.GetInspectorBackend(context_id)
       success = backend.EvaluateJavaScript(

tools/telemetry/telemetry/core/platform/tracing_controller_unittest.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.
+
+from telemetry import decorators
+from telemetry.core.platform import tracing_category_filter
+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()
+    options = tracing_options.TracingOptions()
+    options.enable_chrome_trace = True
+    self._tab.browser.platform.tracing_controller.Start(options,
+                                                        category_filter)
+    self.Navigate('blank.html')
+    self.assertEquals(
+        self._tab.EvaluateJavaScript('document.location.pathname;'),
+        '/blank.html')
+    self._tab.EvaluateJavaScript('console.time = function() { };')
+    with self.assertRaisesRegexp(Exception, 'Page stomped on console.time'):
+      self._tab.browser.platform.tracing_controller.Stop()