Notify about major session changes events.

ash/session_state_delegate.h

Index: ash/session_state_delegate.h
diff --git a/ash/session_state_delegate.h b/ash/session_state_delegate.h
index f0e7f22f42005c677abf234299ce8a4955a7c278..8e7f41a8c8e4a97b62b74766c1669873803ebc58 100644
--- a/ash/session_state_delegate.h
+++ b/ash/session_state_delegate.h
@@ -45,6 +45,27 @@ class ASH_EXPORT SessionStateDelegate {
     CYCLE_TO_PREVIOUS_USER,  // Cycle to the previous user.
   };
 
+  // Defines session state i.e. whether session is running or not and
+  // whether user session is blocked by things like lock screen and
+  // multi-profile login.
+  enum SessionState {
+    STATE_UNKNOWN = 0,
+
+    // When primary user login UI is shown i.e. after boot or sign out,
+    // no active user session exists yet.
+    STATE_LOGIN_PRIMARY,
+
+    // Inside user session, no blocking UI (login/lock) is shown.
+    STATE_SESSION,
+
+    // User session is active, currently is locked.
+    STATE_LOCK,
+
+    // When secondary user login UI is shown i.e. other users are
+    // already logged in and is currently adding another user to the session.
+    STATE_LOGIN_SECONDARY,
+  };
+
   virtual ~SessionStateDelegate() {};
 
   // Returns the browser context for the user given by |index|.