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

test/codegen/expect/sunflower/sunflower.js

 var sunflower;
 (function(exports) {
   'use strict';
   let ORANGE = "orange";
   let SEED_RADIUS = 2;
   let SCALE_FACTOR = 4;
   let TAU = dart.notNull(math.PI) * 2;
   let MAX_D = 300;
   let centerX = dart.notNull(MAX_D) / 2;
   let centerY = centerX;
@@ skipping 29 matching lines @@
       let theta = dart.notNull(i) * dart.notNull(TAU) / dart.notNull(exports.PHI);
       let r = dart.notNull(math.sqrt(i)) * dart.notNull(SCALE_FACTOR);
       let x = dart.notNull(centerX) + dart.notNull(r) * dart.notNull(math.cos(theta));
       let y = dart.notNull(centerY) - dart.notNull(r) * dart.notNull(math.sin(theta));
       new SunflowerSeed(x, y, SEED_RADIUS).draw();
     }
     exports.notes.textContent = `${exports.seeds} seeds`;
   }
   class Circle extends core.Object {
     Circle(x, y, radius) {
-      this.x = x;
-      this.y = y;
-      this.radius = radius;
+      dart.initField(Circle, this, 'x', x);
+      dart.initField(Circle, this, 'y', y);
+      dart.initField(Circle, this, 'radius', radius);
     }
   }
   class CirclePainter extends core.Object {
     CirclePainter() {
-      this.color = ORANGE;
+      dart.initField(CirclePainter, this, 'color', ORANGE);
     }
     draw() {
       exports.context.beginPath();
       exports.context.lineWidth = 2;
       exports.context.fillStyle = this.color;
       exports.context.strokeStyle = this.color;
       exports.context.arc(this.x, this.y, this.radius, 0, TAU, false);
       exports.context.fill();
       exports.context.closePath();
       exports.context.stroke();
@@ skipping 17 matching lines @@
   exports.MAX_D = MAX_D;
   exports.centerX = centerX;
   exports.centerY = centerY;
   exports.querySelector = querySelector;
   exports.main = main;
   exports.draw = draw;
   exports.SunflowerSeed = SunflowerSeed;
   exports.Circle = Circle;
   exports.CirclePainter = CirclePainter;
 })(sunflower || (sunflower = {}));