Make sure async event contains tts data.

BUG=

Review URL: https://codereview.chromium.org/299833009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272461 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/timeline/trace_event_importer.py

@@ -345,6 +345,7 @@ class TraceEventTimelineImporter(importer.TimelineImporter):
           async_slice.end_thread = async_event_state['thread']
           if async_slice.start_thread == async_slice.end_thread:
             if 'tts' in event and 'tts' in events[0]['event']:
+              async_slice.thread_start = events[0]['event']['tts'] / 1000.0
               async_slice.thread_duration = ((event['tts'] / 1000.0)
                   - (events[0]['event']['tts'] / 1000.0))
           async_slice.id = event_id

tools/telemetry/telemetry/core/timeline/trace_event_importer_unittest.py

@@ -945,6 +945,8 @@ class TraceEventTimelineImporterTest(unittest.TestCase):
     self.assertEqual('a', parent_slice.name)
     self.assertEqual('foo', parent_slice.category)
     self.assertEqual(0, parent_slice.start)
+    self.assertAlmostEqual(17/1000.0, parent_slice.thread_start)
+    self.assertAlmostEqual(25/1000.0, parent_slice.thread_end)
 
     self.assertEqual(2, len(parent_slice.sub_slices))
     sub_slice = parent_slice.sub_slices[0]