Make empty traces a non-critical error

Its okay for a trace to come back with no data in it. Right now,
this actually causes catastrophic failure.

R=tonyg

Review URL: https://codereview.chromium.org/141553009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247924 0039d316-1c4b-4281-b951-d872f2087c98

tools/telemetry/telemetry/core/timeline/empty_trace_importer.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.
+
+class EmptyTraceImporter(object):
+  """Imports empty traces."""
+  def __init__(self, model, event_data, import_priority=0):
+    pass
+
+  @staticmethod
+  def CanImport(event_data):
+    if isinstance(event_data, list):
+      return len(event_data) == 0
+    elif isinstance(event_data, basestring):
+      return len(event_data) == 0
+    return False
+
+  def ImportEvents(self):
+    pass
+
+  def FinalizeImport(self):
+    pass

tools/telemetry/telemetry/core/timeline/model.py

@@ -15,11 +15,13 @@ from telemetry.core import web_contents
 from telemetry.core import browser
 
 # Register importers for data
-from telemetry.core.timeline import inspector_importer
 from telemetry.core.timeline import bounds
+from telemetry.core.timeline import empty_trace_importer
+from telemetry.core.timeline import inspector_importer
 from telemetry.core.timeline import trace_event_importer
 
 _IMPORTERS = [
+    empty_trace_importer.EmptyTraceImporter,
     inspector_importer.InspectorTimelineImporter,
     trace_event_importer.TraceEventTimelineImporter
 ]

tools/telemetry/telemetry/core/timeline/model_unittest.py

-# Copyright (c) 2013 The Chromium Authors. All rights reserved.
+# Copyright (c) 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 unittest
 
+from telemetry.core.timeline import model
+
 class TimelineModelUnittest(unittest.TestCase):
-  pass
+  def testEmptyImport(self):
+    model.TimelineModel([])
+    model.TimelineModel('')