Make empty traces a non-critical error

tools/telemetry/telemetry/core/timeline/empty_trace_importer.py

Index: tools/telemetry/telemetry/core/timeline/empty_trace_importer.py
diff --git a/tools/telemetry/telemetry/core/timeline/empty_trace_importer.py b/tools/telemetry/telemetry/core/timeline/empty_trace_importer.py
new file mode 100644
index 0000000000000000000000000000000000000000..925ee6b67d0c04971fa714496191e55f56a7cc08
--- /dev/null
+++ b/tools/telemetry/telemetry/core/timeline/empty_trace_importer.py
@@ -0,0 +1,22 @@
+# 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.
+
+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