Stop bad results on first memory benchmark run

tools/perf/benchmarks/system_health.py

 # Copyright 2016 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 re
 
 from benchmarks import page_cycler_v2
 
 from core import perf_benchmark
 
@@ skipping 87 matching lines @@
     options.SetTimelineBasedMetrics(['memoryMetric'])
     # Setting an empty memory dump config disables periodic dumps.
     options.config.chrome_trace_config.SetMemoryDumpConfig(
         chrome_trace_config.MemoryDumpConfig())
     return options
 
   def CreateStorySet(self, options):
     return page_sets.SystemHealthStorySet(platform=self.PLATFORM,
                                           take_memory_measurement=True)
 
+  def SetExtraBrowserOptions(self, options):
+    # Just before we measure memory we flush the system caches
+    # unfortunately this doesn't immediately take effect, instead
+    # the next story run is effected. Due to this the first story run
+    # has anomalous results. This option causes us to flush caches
+    # each time before Chrome starts so we effect even the first story
+    # - avoiding the bug.
+    options.clear_sytem_cache_for_browser_and_profile_on_start = True
+
   @classmethod
   def ShouldTearDownStateAfterEachStoryRun(cls):
     return True
 
   @classmethod
   def Name(cls):
     return 'system_health.memory_%s' % cls.PLATFORM
 
   @classmethod
   def ValueCanBeAddedPredicate(cls, value, is_first_result):
@@ skipping 67 matching lines @@
   and load a blank page with multiprocess enabled.
   """
 
   def SetExtraBrowserOptions(self, options):
     options.AppendExtraBrowserArgs(
         ['--webview-sandboxed-renderer'])
 
   @classmethod
   def Name(cls):
     return 'system_health.webview_startup_multiprocess'