Fix import order with isort tool.

tools/telemetry/telemetry/core/heap/model.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.
 
 from telemetry.core.heap import chrome_js_heap_snapshot_parser
 
+
 class Model(object):
   """ The heap snapshot model is a set of LiveHeapObjects. The LiveHeapObjects
   contain the RetainingEdge objects describing the relationships between the
   LiveHeapObjects."""
 
   def __init__(self, raw_data):
     if not chrome_js_heap_snapshot_parser.ChromeJsHeapSnapshotParser.CanImport(
         raw_data):
       raise ValueError("Cannot import snapshot data")
     parser = chrome_js_heap_snapshot_parser.ChromeJsHeapSnapshotParser(raw_data)
     self._all_live_heap_objects = parser.GetAllLiveHeapObjects()
 
   @property
   def all_live_heap_objects(self):
     return self._all_live_heap_objects