Add multi_profile_user_count field to system_profile proto.

chrome/browser/metrics/metrics_log.h

Index: chrome/browser/metrics/metrics_log.h
diff --git a/chrome/browser/metrics/metrics_log.h b/chrome/browser/metrics/metrics_log.h
index fe06b61f03caf343887f796cef4c3929256e6ef5..4d9d1365309e42e224429985f56251a33fb1324b 100644
--- a/chrome/browser/metrics/metrics_log.h
+++ b/chrome/browser/metrics/metrics_log.h
@@ -184,6 +184,13 @@ class MetricsLog : public MetricsLogBase {
   // This is a no-op if called on a non-Chrome OS platform.
   void WriteBluetoothProto(metrics::SystemProfileProto::Hardware* hardware);
 
+#if defined(OS_CHROMEOS)
+  // Update the number of users logged into a multi-profile session.
+  // If the number of users change while the log is open, we invalidate

[Ilya Sherman, 2013/10/08 01:31:03]

nit: "we invalidate" -> "the call invalidates" or some other phrasing without
"we" is preferred.

[Tim Song, 2013/10/08 20:29:40]

Done.

+  // the value.
+  void UpdateMultiProfileUserCount();
+#endif
+
   // Observes network state to provide values for SystemProfile::Network.
   MetricsNetworkObserver network_observer_;