Heartbeat: Reduce the heartbeat from 120 sec to 100 sec when the window doesn't have the focus, to be shorter than the post lock expiration window.

props azaozz.
fixes #24894.



git-svn-id: https://develop.svn.wordpress.org/trunk@24908 602fd350-edb4-49c9-b593-d223f7449a82

wp-includes/js/heartbeat.js

@@ -225,7 +225,7 @@ window.wp = window.wp || {};
 				return;
 
 			if ( ! hasFocus ) {
-				t = 120000; // 2 min
+				t = 100000; // 100 sec. Post locks expire after 120 sec.
 			} else if ( countdown > 0 && tempInterval ) {
 				t = tempInterval;
 				countdown--;