metalet with postfix improvement

lib/runtime/dart/collection.js

Index: lib/runtime/dart/collection.js
diff --git a/lib/runtime/dart/collection.js b/lib/runtime/dart/collection.js
index 1a0ebb176efa5dfc434ad6824fa1540ac1f88531..6edcc2b5daa60c00f7a400d69525cb48e8f21c32 100644
--- a/lib/runtime/dart/collection.js
+++ b/lib/runtime/dart/collection.js
@@ -1505,19 +1505,11 @@ var collection;
         return result;
       }
       [core.$add](element) {
-        this[core.$set]((() => {
-          let o$ = this, x$ = o$[core.$length];
-          o$[core.$length] = dart.notNull(x$) + 1;
-          return x$;
-        }).bind(this)(), element);
+        this[core.$set](dart.prop(this, 'length').notNull++, element);
       }
       [core.$addAll](iterable) {
         for (let element of iterable) {
-          this[core.$set]((() => {
-            let o$ = this, x$ = o$[core.$length];
-            o$[core.$length] = dart.notNull(x$) + 1;
-            return x$;
-          }).bind(this)(), element);
+          this[core.$set](dart.prop(this, 'length').notNull++, element);
         }
       }
       [core.$remove](element) {
@@ -1724,8 +1716,7 @@ var collection;
         }
         if (!(typeof index == 'number'))
           throw new core.ArgumentError(index);
-        let o$ = this;
-        o$[core.$length] = dart.notNull(o$[core.$length]) + 1;
+        dart.prop(this, 'length').notNull++;
         this.setRange(dart.notNull(index) + 1, this[core.$length], this, index);
         this[core.$set](index, element);
       }