Reland [telemetry] Timeline model cleanups

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

Index: tools/telemetry/telemetry/core/timeline/tracing/async_slice.py
diff --git a/tools/telemetry/telemetry/core/timeline/tracing/async_slice.py b/tools/telemetry/telemetry/core/timeline/tracing/async_slice.py
deleted file mode 100644
index 03031c1e6e43bb5afdcd66c5444f37086507a965..0000000000000000000000000000000000000000
--- a/tools/telemetry/telemetry/core/timeline/tracing/async_slice.py
+++ /dev/null
@@ -1,21 +0,0 @@
-# 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.tracing.slice as tracing_slice
-
-class AsyncSlice(tracing_slice.Slice):
-  ''' 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, parent=None):
-    super(AsyncSlice, self).__init__(
-        category, name, timestamp, args=args, parent=parent)
-    self.start_thread = None
-    self.end_thread = None
-    self.id = None
-
-  def AddSubSlice(self, sub_slice):
-    super(AsyncSlice, self).AddSubSlice(sub_slice)
-    self.children.append(sub_slice)