Remove the weak dictionary that maps tab objects to it markers

tools/perf/measurements/thread_times.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.
 from measurements import timeline_controller
 from metrics import timeline
 from telemetry.core.backends.chrome import tracing_backend
 from telemetry.page import page_measurement
 
 class ThreadTimes(page_measurement.PageMeasurement):
   def __init__(self):
@@ skipping 21 matching lines @@
       self._timeline_controller.trace_categories = \
           tracing_backend.MINIMAL_TRACE_CATEGORIES
     self._timeline_controller.Start(page, tab)
 
   def DidRunActions(self, page, tab):
     self._timeline_controller.Stop(tab)
 
   def MeasurePage(self, page, tab, results):
     metric = timeline.ThreadTimesTimelineMetric()
     renderer_thread = \
-        self._timeline_controller.model.GetRendererThreadFromTab(tab)
+        self._timeline_controller.model.GetRendererThreadFromTabId(tab.id)
     if self.options.report_silk_results:
       metric.results_to_report = timeline.ReportSilkResults
     if self.options.report_silk_details:
       metric.details_to_report = timeline.ReportSilkDetails
     metric.AddResults(self._timeline_controller.model, renderer_thread,
                       self._timeline_controller.smooth_records, results)
 
   def CleanUpAfterPage(self, _, tab):
     self._timeline_controller.CleanUp(tab)