[tools/perf] Reference legacy_page_test module instead of page_test

tools/perf/measurements/v8_gc_times.py

 # Copyright 2015 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.page import page_test
+from telemetry.page import legacy_page_test
 from telemetry.timeline.model import TimelineModel
 from telemetry.timeline import tracing_config
 from telemetry.util import statistics
 from telemetry.value import scalar
 
 
-class V8GCTimes(page_test.PageTest):
+class V8GCTimes(legacy_page_test.LegacyPageTest):
 
   _TIME_OUT_IN_SECONDS = 60
   _CATEGORIES = ['blink.console',
                  'renderer.scheduler',
                  'v8',
                  'webkit.console']
   _RENDERER_MAIN_THREAD = 'CrRendererMain'
   _IDLE_TASK_PARENT = 'SingleThreadIdleTaskRunner::RunTask'
 
   def __init__(self):
@@ skipping 206 matching lines @@
     self.count = 0
 
   @property
   def thread_duration_outside_idle(self):
     return self.thread_duration - self.thread_duration_inside_idle
 
   @property
   def percentage_thread_duration_during_idle(self):
     return statistics.DivideIfPossibleOrZero(
         100 * self.thread_duration_inside_idle, self.thread_duration)