+ // If the specified WebContents has a SessionTabHelper (probably because it
+ // was used as the contents of a tab), returns a tab id. This value is
+ // immutable for a given tab. It will be unique across Chrome within the
+ // current session, but may be re-used across sessions. Returns -1
+ // for a NULL WebContents or if the WebContents has no SessionTabHelper.
+ static SessionID::id_type IdForTab(const content::WebContents* tab);
+
+ // If the specified WebContents has a SessionTabHelper (probably because it
+ // was used as the contents of a tab), and has ever been attached to a Browser
+ // window, returns Browser::session_id().id() for that Browser. If the tab is
+ // being dragged between Browser windows, returns the old window's id value.
+ // If the WebContents has a SessionTabHelper but has never been attached to a
+ // Browser window, returns an id value that is different from that of any
+ // Browser. Returns -1 for a NULL WebContents or if the WebContents has no
+ // SessionTabHelper.
+ static SessionID::id_type IdForWindowContainingTab(
+ const content::WebContents* tab);
+