Measure private dirty memory on OS that have /proc (e.g. Linux).

tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py

Index: tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
diff --git a/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py b/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
index aabeba11cdedecdc592dfa012a93eeaad9ec4aa1..8a7ddd0d81593fd16f8825b97c2a98c684106e4b 100644
--- a/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
+++ b/tools/telemetry/telemetry/core/platform/proc_supporting_platform_backend.py
@@ -59,8 +59,15 @@ class ProcSupportingPlatformBackend(platform_backend.PlatformBackend):
     wss = int(stats[23]) * resource.getpagesize()
     wss_peak = (self._ConvertKbToByte(status['VmHWM'])
                 if 'VmHWM' in status else wss)
+
+    private_dirty_bytes = 0
+    for line in self._GetProcFileForPid(pid, 'smaps').splitlines():
+      if line.startswith('Private_Dirty:'):
+        private_dirty_bytes += self._ConvertKbToByte(line.split(':')[1].strip())
+
     return {'VM': vm,
             'VMPeak': vm_peak,
+            'PrivateDirty': private_dirty_bytes,
             'WorkingSetSize': wss,
             'WorkingSetSizePeak': wss_peak}