timers: make previous change simpler

Instead of adding a property on the list of timers, simply compare the
current value of what represents the current time if its value is
earlier than the time of the current timer being processed.

lib/timers.js

@@ -83,10 +83,6 @@ function listOnTimeout() {
   debug('timeout callback ' + msecs);
 
   var now = Timer.now();
-  // now's value has been updated, consider that it doesn't need to be updated
-  // unless a timer is added within the loop that processes the timers list
-  // below
-  list._addedTimer = false;
   debug('now: %d', now);
 
   var first;
@@ -95,10 +91,9 @@ function listOnTimeout() {
     // update the value of "now" so that timing computations are
     // done correctly. See test/simple/test-timers-blocking-callback.js
     // for more information.
-    if (list._addedTimer) {
+    if (now < first._monotonicStartTime) {
       now = Timer.now();
       debug('now: %d', now);
-      list._addedTimer = false;
     }
 
     var diff = now - first._monotonicStartTime;
@@ -198,12 +193,6 @@ exports.active = function(item) {
     }
 
     list = lists[msecs];
-    // Set _addedTimer so that listOnTimeout can refresh
-    // its current time value to avoid wrong timing computation
-    // in case timers callback block for a while.
-    // See test/simple/test-timers-blocking-callback.js for more
-    // details
-    list._addedTimer = true;
   }
 };