introduce functions (#3360)

`var f = function() {};` => `function f() {}`

lib/scope.js

@@ -333,7 +333,7 @@ function next_mangled_name(scope, options, def) {
         } while (scope = scope.parent_scope);
     });
     var name;
-    for (var i = 0, len = holes.length; i < len; i++) {
+    for (var i = 0; i < holes.length; i++) {
         name = base54(holes[i]);
         if (names[name]) continue;
         holes.splice(i, 1);
@@ -555,7 +555,7 @@ var base54 = (function() {
     var freq = Object.create(null);
     function init(chars) {
         var array = [];
-        for (var i = 0, len = chars.length; i < len; i++) {
+        for (var i = 0; i < chars.length; i++) {
             var ch = chars[i];
             array.push(ch);
             freq[ch] = -1e-2 * i;