Use MessageChannel-based nextTick to schedule Editor display update

This is the fastest way I've found to get the nextTick behavior, which allows us to aggregate multiple requests for display update (from selection changes, cursor movement, line changes) etc into a single call at the end of processing an event.

src/app/editor.coffee

@@ -734,7 +734,7 @@ class Editor extends View
   requestDisplayUpdate: ()->
     return if @pendingDisplayUpdate
     @pendingDisplayUpdate = true
-    webkitRequestAnimationFrame =>
+    _.nextTick =>
       @updateDisplay()
       @pendingDisplayUpdate = false
 

src/stdlib/underscore-extensions.coffee

@@ -71,4 +71,14 @@ _.mixin
     inverted
 
   multiplyString: (string, n) ->
-    new Array(1 + n).join(string)
+    new Array(1 + n).join(string)
+
+  nextTick: (fn) ->
+    unless @messageChannel
+      @pendingNextTickFns = []
+      @messageChannel = new MessageChannel
+      @messageChannel.port1.onmessage = =>
+        fn() while fn = @pendingNextTickFns.shift()
+
+    @pendingNextTickFns.push(fn)
+    @messageChannel.port2.postMessage(0)