[system-health] Only flush system cache on mobile

tools/perf/benchmarks/system_health.py

Index: tools/perf/benchmarks/system_health.py
diff --git a/tools/perf/benchmarks/system_health.py b/tools/perf/benchmarks/system_health.py
index 75a688132d0dc67786a4f7aebe94736de9c0540e..2b013a55d969de3a2e8ba89bada91111a547542a 100644
--- a/tools/perf/benchmarks/system_health.py
+++ b/tools/perf/benchmarks/system_health.py
@@ -105,15 +105,6 @@ class _MemorySystemHealthBenchmark(perf_benchmark.PerfBenchmark):
     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
@@ -153,6 +144,15 @@ class MobileMemorySystemHealth(_MemorySystemHealthBenchmark):
 
     return possible_browser.platform.GetDeviceTypeName() == 'Desktop'
 
+  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
+
 
 @benchmark.Enabled('android-webview')
 class WebviewStartupSystemHealthBenchmark(perf_benchmark.PerfBenchmark):