[telemetry] Implement first version of timeline based measurement

tools/telemetry/telemetry/core/timeline/async_slice.py

 # Copyright 2013 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 telemetry.core.timeline.event as event
 
 class AsyncSlice(event.TimelineEvent):
   ''' A AsyncSlice represents an interval of time during which an
   asynchronous operation is in progress. An AsyncSlice consumes no CPU time
   itself and so is only associated with Threads at its start and end point.
   '''
-  def __init__(self, category, name, timestamp, args=None):
+  def __init__(self, category, name, timestamp, args=None,
+               duration=0, start_thread=None, end_thread=None):
     super(AsyncSlice, self).__init__(
-        category, name, timestamp, duration=0, args=args)
+        category, name, timestamp, duration=duration, args=args)
     self.parent_slice = None
-    self.start_thread = None
-    self.end_thread = None
+    self.start_thread = start_thread
+    self.end_thread = end_thread
     self.sub_slices = []
     self.id = None
 
   def AddSubSlice(self, sub_slice):
     assert sub_slice.parent_slice == self
     self.sub_slices.append(sub_slice)
 
 
   def IterEventsInThisContainerRecrusively(self):
     for sub_slice in self.sub_slices:
       yield sub_slice