[Telemetry] Add the ability to flush the system file cache to platform.

tools/telemetry/telemetry/core/platform/android_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/android_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/android_platform_backend.py b/tools/telemetry/telemetry/core/platform/android_platform_backend.py
index ccde44df5f73f741966d538abba2851beaf26b23..12f74c3fc43ee93535bde61779572c75165524c6 100644
--- a/tools/telemetry/telemetry/core/platform/android_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/android_platform_backend.py
@@ -6,6 +6,7 @@ import logging
 import os
 import sys
 
+from telemetry.core import perf_tests_helper
 from telemetry.core import platform
 from telemetry.core.platform import platform_backend
 
@@ -122,3 +123,13 @@ class AndroidPlatformBackend(platform_backend.PlatformBackend):
 
   def GetOSName(self):
     return 'android'
+
+  def CanFlushIndividualFilesFromSystemCache(self):
+    return False
+
+  def FlushEntireSystemCache(self):
+    cache_control = perf_tests_helper.CacheControl(self._adb.Adb())
+    cache_control.DropRamCaches()
+
+  def FlushSystemCacheForDirectory(self, directory, ignoring=None):
+    raise NotImplementedError()