Revert "Partially migrate from old getter syntax to new one."

lib/dom/templates/html/dart2js/impl_MouseEvent.darttemplate

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 $!MEMBERS
 
-  int get offsetX {
+  int get offsetX() {
     if (JS('bool', '!!this.offsetX')) {
       return this._offsetX;
     } else {
       // Firefox does not support offsetX.
       var target = this.target;
       if (!(target is Element)) {
         throw const UnsupportedOperationException(
             'offsetX is only supported on elements');
       }
       return this.clientX - this.target.$dom_getBoundingClientRect().left;
     }
   }
 
-  int get offsetY {
+  int get offsetY() {
     if (JS('bool', '!!this.offsetY')) {
       return this._offsetY;
     } else {
       // Firefox does not support offsetY.
       var target = this.target;
       if (!(target is Element)) {
         throw const UnsupportedOperationException(
             'offsetX is only supported on elements');
       }
       return this.clientY - this.target.$dom_getBoundingClientRect().top;
     }
   }
 
-  int get _offsetX native 'return this.offsetX';
-  int get _offsetY native 'return this.offsetY';
+  int get _offsetX() native 'return this.offsetX';
+  int get _offsetY() native 'return this.offsetY';
 }