cros: Add enterprise user session metrics

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index 5c8d693edf3aafb7e68a88ccf8f63af156379a8d..978b133eff3e9bb3bbe9f09cb408e865d468accc 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -727,6 +727,14 @@ const char kSessionLengthLimit[] = "session.length_limit";
 const char kSessionWaitForInitialUserActivity[] =
     "session.wait_for_initial_user_activity";
 
+// A preference of the last user session type. It is used with the
+// kLastSessionLength pref below to store the last user session info
+// on shutdown so that it could be reported on the next run.
+const char kLastSessionType[] = "session.last_session_type";
+
+// A preference of the last user session length.
+const char kLastSessionLength[] = "session.last_session_length";
+
 // Inactivity time in milliseconds while the system is on AC power before
 // the screen should be dimmed, turned off, or locked, before an
 // IdleActionImminent D-Bus signal should be sent, or before