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

lib/runtime/dart/math.js

Index: lib/runtime/dart/math.js
diff --git a/lib/runtime/dart/math.js b/lib/runtime/dart/math.js
index ad6a382788c631272f5522865eea3cd80bf41e33..7a960393cb5adacb09848731ec6013fd6ce19929 100644
--- a/lib/runtime/dart/math.js
+++ b/lib/runtime/dart/math.js
@@ -22,8 +22,8 @@ var math;
   let Point$ = dart.generic(function(T) {
     class Point extends core.Object {
       Point(x, y) {
-        this.x = x;
-        this.y = y;
+        dart.initField(Point, this, 'x', x);
+        dart.initField(Point, this, 'y', y);
       }
       toString() {
         return `Point(${this.x}, ${this.y})`;
@@ -137,10 +137,10 @@ var math;
   let Rectangle$ = dart.generic(function(T) {
     class Rectangle extends _RectangleBase$(T) {
       Rectangle(left, top, width, height) {
-        this.left = left;
-        this.top = top;
-        this.width = dart.as(width['<'](0) ? dart.notNull(width['unary-']()) * 0 : width, T);
-        this.height = dart.as(height['<'](0) ? dart.notNull(height['unary-']()) * 0 : height, T);
+        dart.initField(Rectangle, this, 'left', left);
+        dart.initField(Rectangle, this, 'top', top);
+        dart.initField(Rectangle, this, 'width', dart.as(width['<'](0) ? dart.notNull(width['unary-']()) * 0 : width, T));
+        dart.initField(Rectangle, this, 'height', dart.as(height['<'](0) ? dart.notNull(height['unary-']()) * 0 : height, T));
         super._RectangleBase();
       }
       fromPoints(a, b) {
@@ -160,8 +160,8 @@ var math;
   let MutableRectangle$ = dart.generic(function(T) {
     class MutableRectangle extends _RectangleBase$(T) {
       MutableRectangle(left, top, width, height) {
-        this.left = left;
-        this.top = top;
+        dart.initField(MutableRectangle, this, 'left', left);
+        dart.initField(MutableRectangle, this, 'top', top);
         this[_width] = dart.as(width['<'](0) ? _clampToZero(width) : width, T);
         this[_height] = dart.as(height['<'](0) ? _clampToZero(height) : height, T);
         super._RectangleBase();