perf: Make RAF heavy first frame test do what it says

tools/perf/page_sets/tough_scheduling_cases.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 telemetry.page import page as page_module
 from telemetry.page import page_set as page_set_module
 
 
 class ToughSchedulingCasesPage(page_module.Page):
 
   def __init__(self, url, page_set):
@@ skipping 231 matching lines @@
 
 class Page16(ToughSchedulingCasesPage):
 
   """ Why: Test a requestAnimationFrame handler with a heavy first frame """
 
   def __init__(self, page_set):
     super(Page16, self).__init__(
       url='file://tough_scheduling_cases/raf.html?heavy_first_frame',
       page_set=page_set)
 
-    self.synthetic_delays = {'cc.BeginMainFrame': {'target_duration': 0.15}}
+    self.synthetic_delays = {'cc.BeginMainFrame': {'target_duration': 0.15,
+                                                   'mode': 'oneshot'}}
 
 
 class Page17(ToughSchedulingCasesPage):
 
   """ Why: Medium stress test for the scheduler """
 
   def __init__(self, page_set):
     super(Page17, self).__init__(
       url='file://tough_scheduling_cases/raf_touch_animation.html?medium',
       page_set=page_set)
@@ skipping 195 matching lines @@
     # Why: Scroll bounce with slow handler on desktop, blocks only once until
     # ACK timeout.
     self.AddPage(EmptyTouchHandlerPage(
       name='bounce_desktop_slow_handler',
       desktop=True,
       slow_handler=True,
       bounce=True,
       page_set=self))
     # Why: For measuring the latency of scroll-synchronized effects.
     self.AddPage(SynchronizedScrollOffsetPage(page_set=self))