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

tools/telemetry/telemetry/core/platform/cros_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/cros_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/cros_platform_backend.py b/tools/telemetry/telemetry/core/platform/cros_platform_backend.py
index 68ecc34a4ad816f469dbd3112603b7cdd5bf7869..3c0a25c70693fa599bd2d9506f918f5ae95e640b 100644
--- a/tools/telemetry/telemetry/core/platform/cros_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/cros_platform_backend.py
@@ -2,10 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-from telemetry.core.platform import linux_platform_backend
+from telemetry.core.platform import platform_backend
+from telemetry.core.platform import proc_util
 
 
-class CrosPlatformBackend(linux_platform_backend.LinuxPlatformBackend):
+class CrosPlatformBackend(platform_backend.PlatformBackend):
 
   def __init__(self, cri):
     super(CrosPlatformBackend, self).__init__()
@@ -35,6 +36,15 @@ class CrosPlatformBackend(linux_platform_backend.LinuxPlatformBackend):
     except AssertionError:
       return ''
 
+  def GetSystemCommitCharge(self):
+    meminfo_contents = self._GetFileContents('/proc/meminfo')
+    return proc_util.GetSystemCommitCharge(meminfo_contents)
+
+  def GetMemoryStats(self, pid):
+    status = self._GetFileContents('/proc/%s/status' % pid)
+    stats = self._GetFileContents('/proc/%s/stat' % pid).split()
+    return proc_util.GetMemoryStats(status, stats)
+
   def GetIOStats(self, pid):
     # There is no '/proc/<pid>/io' file on CrOS platforms
     # Returns empty dict as it does in PlatformBackend.
@@ -42,3 +52,12 @@ class CrosPlatformBackend(linux_platform_backend.LinuxPlatformBackend):
 
   def GetOSName(self):
     return 'chromeos'
+
+  def CanFlushIndividualFilesFromSystemCache(self):
+    return True
+
+  def FlushEntireSystemCache(self):
+    raise NotImplementedError()
+
+  def FlushSystemCacheForDirectory(self, directory, ignoring=None):
+    raise NotImplementedError()