Implement FlushSystemCacheForDirectory for Chrome OS

tools/telemetry/telemetry/core/platform/__init__.py

Index: tools/telemetry/telemetry/core/platform/__init__.py
diff --git a/tools/telemetry/telemetry/core/platform/__init__.py b/tools/telemetry/telemetry/core/platform/__init__.py
index fab8a1beaab9ce0967750943cc8066e02762e400..fde62ec886be0efb7cea1aae764a707c4d4f2834 100644
--- a/tools/telemetry/telemetry/core/platform/__init__.py
+++ b/tools/telemetry/telemetry/core/platform/__init__.py
@@ -182,15 +182,14 @@ class Platform(object):
     This function may require root or administrator access."""
     return self._platform_backend.FlushEntireSystemCache()
 
-  def FlushSystemCacheForDirectory(self, directory, ignoring=None):
+  def FlushSystemCacheForDirectory(self, directory):
     """Flushes the OS's file cache for the specified directory.
 
     Any files or directories inside |directory| matching a name in the
     |ignoring| list will be skipped.
 
     This function does not require root or administrator access."""
-    return self._platform_backend.FlushSystemCacheForDirectory(
-        directory, ignoring=ignoring)
+    return self._platform_backend.FlushSystemCacheForDirectory(directory)
 
   def FlushDnsCache(self):
     """Flushes the OS's DNS cache completely.