Added unit test for stack traces in telemetry crashes.

tools/perf/core/stacktrace_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.core import exceptions
+from telemetry import decorators
+from telemetry.testing import tab_test_case
+
+class TabStackTraceTest(tab_test_case.TabTestCase):
+
+  # Currently stack traces do not work on windows: http://crbug.com/476110
+  # Linux stack traces depends on fission support: http://crbug.com/405623
+  @decorators.Enabled('mac')

[nednguyen, 2015/12/17 02:26:54]

Add: @decorators.Isolated so that this test is not run in parallel with other
telemetry test that also invokes browser.

[David Yen, 2015/12/21 17:47:50]

Hmm, I've added this now but that's a little bit worrisome because it means
stack traces will be racey and might not show the right stack.

+  def testCrashSymbols(self):
+    try:

[nednguyen, 2015/12/17 02:26:54]

Maybe you need to clear
out/Release/Chromium.app/Contents/Versions/49.0.2594.0/Chromium
Framework.framework/Chromium Framework directory first?

[David Yen, 2015/12/21 17:47:50]

That file is part of the executable so that shouldn't be the racey part. I
suspect it is probably the crash dumps themselves. I believe last time I looked
into this it just looked in the crash dump directory and looked for the latest
one.

+      self._tab.Navigate('chrome://crash', timeout=5)
+    except exceptions.DevtoolsTargetCrashException as e:
+      self.assertTrue('CrashIntentionally' in '\n'.join(e.stack_trace))

[nednguyen, 2015/12/17 01:52:45]

self.assertIn('CrashIntentionally', '\n'.join(e.stack_trace)) so when this
fails, the exception message will tell you what is in the 2nd argument.

[David Yen, 2015/12/21 17:47:50]

Done.