Stop bad results on first memory benchmark run

tools/perf/benchmarks/memory.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.
 
 import re
 
 from core import perf_benchmark
 
 from telemetry import benchmark
 from telemetry.timeline import chrome_trace_category_filter
@@ skipping 23 matching lines @@
         filter_string='-*,blink.console,disabled-by-default-memory-infra')
     tbm_options = timeline_based_measurement.Options(
         overhead_level=trace_memory)
     tbm_options.config.enable_android_graphics_memtrack = True
     tbm_options.SetTimelineBasedMetrics(['memoryMetric'])
     # Setting an empty memory dump config disables periodic dumps.
     tbm_options.config.chrome_trace_config.SetMemoryDumpConfig(
         chrome_trace_config.MemoryDumpConfig())
     return tbm_options
 
+  def SetExtraBrowserOptions(self, options):
+    # Just before we measure memory we flush the system caches
+    # unfortunately this doesn't immediately take effect, instead
+    # the next page run is effected. Due to this the first page run
+    # has anomalous results. This option causes us to flush caches
+    # each time before Chrome starts so we effect even the first page
+    # - avoiding the bug.
+    options.clear_sytem_cache_for_browser_and_profile_on_start = True
+
 
 # TODO(bashi): Workaround for http://crbug.com/532075.
 # @benchmark.Enabled('android') shouldn't be needed.
 @benchmark.Enabled('android')
 class MemoryBenchmarkTop10Mobile(_MemoryInfra):
   """Measure foreground/background memory on top 10 mobile page set.
 
   This metric provides memory measurements for the System Health Plan of
   Chrome on Android.
   """
@@ skipping 185 matching lines @@
   of long running idle Gmail page """
   page_set = page_sets.LongRunningIdleGmailBackgroundPageSet
 
   @classmethod
   def Name(cls):
     return 'memory.long_running_idle_gmail_background_tbmv2'
 
   @classmethod
   def ShouldDisable(cls, possible_browser):  # http://crbug.com/616530
     return cls.IsSvelte(possible_browser)