fixes #52, fields shadowing getters/setters or other fields

test/codegen/expect/sunflower/dom.js

 var dom;
 (function(exports) {
   'use strict';
   class JsName extends core.Object {
     JsName(opts) {
       let name = opts && 'name' in opts ? opts.name : null;
-      this.name = name;
+      dart.initField(JsName, this, 'name', name);
     }
   }
   class Overload extends core.Object {
     Overload() {
     }
   }
   let overload = new Overload();
   let EventListener = dart.typedef('EventListener', () => dart.functionType(dart.void, [Event]));
   class Event extends core.Object {}
   let InputElement = HTMLInputElement;
   let CanvasElement = HTMLCanvasElement;
   class RenderingContext extends core.Object {}
   class CanvasDrawingStyles extends core.Object {
     CanvasDrawingStyles() {
-      this.lineWidth = null;
-      this.lineCap = null;
-      this.lineJoin = null;
-      this.miterLimit = null;
-      this.lineDashOffset = null;
-      this.font = null;
-      this.textAlign = null;
-      this.textBaseline = null;
+      dart.initField(CanvasDrawingStyles, this, 'lineWidth', null);
+      dart.initField(CanvasDrawingStyles, this, 'lineCap', null);
+      dart.initField(CanvasDrawingStyles, this, 'lineJoin', null);
+      dart.initField(CanvasDrawingStyles, this, 'miterLimit', null);
+      dart.initField(CanvasDrawingStyles, this, 'lineDashOffset', null);
+      dart.initField(CanvasDrawingStyles, this, 'font', null);
+      dart.initField(CanvasDrawingStyles, this, 'textAlign', null);
+      dart.initField(CanvasDrawingStyles, this, 'textBaseline', null);
     }
   }
   class CanvasPathMethods extends core.Object {}
   // Exports:
   exports.JsName = JsName;
   exports.Overload = Overload;
   exports.overload = overload;
   exports.EventListener = EventListener;
   exports.Event = Event;
   exports.InputElement = InputElement;
   exports.CanvasElement = CanvasElement;
   exports.RenderingContext = RenderingContext;
   exports.CanvasDrawingStyles = CanvasDrawingStyles;
   exports.CanvasPathMethods = CanvasPathMethods;
 })(dom || (dom = window));