Typecheck constructor initializers properly

test/codegen/expect/math/math.js

 var math;
 (function(math) {
   'use strict';
   let E = 2.718281828459045;
   let LN10 = 2.302585092994046;
   let LN2 = 0.6931471805599453;
   let LOG2E = 1.4426950408889634;
   let LOG10E = 0.4342944819032518;
   let PI = 3.141592653589793;
   let SQRT1_2 = 0.7071067811865476;
@@ skipping 339 matching lines @@
       }
     }
     return _RectangleBase;
   });
   let _RectangleBase = _RectangleBase$(dynamic);
   let Rectangle$ = dart.generic(function(T) {
     class Rectangle extends _RectangleBase$(T) {
       Rectangle(left, top, width, height) {
         this.left = left;
         this.top = top;
-        this.width = width['<'](0) ? dart.notNull(dart.throw_("Unimplemented PrefixExpression: -width")) * 0 : width;
-        this.height = height['<'](0) ? dart.notNull(dart.throw_("Unimplemented PrefixExpression: -height")) * 0 : height;
+        this.width = dart.as(width['<'](0) ? dart.notNull(dart.throw_("Unimplemented PrefixExpression: -width")) * 0 : width, T);
+        this.height = dart.as(height['<'](0) ? dart.notNull(dart.throw_("Unimplemented PrefixExpression: -height")) * 0 : height, T);
         super._RectangleBase();
       }
       Rectangle$fromPoints(a, b) {
         let left = dart.as(min(a.x, b.x), T);
         let width = dart.as(core.num['-'](max(a.x, b.x), left), T);
         let top = dart.as(min(a.y, b.y), T);
         let height = dart.as(core.num['-'](max(a.y, b.y), top), T);
         return new Rectangle(left, top, width, height);
       }
     }
     dart.defineNamedConstructor(Rectangle, 'fromPoints');
     return Rectangle;
   });
   let Rectangle = Rectangle$(dynamic);
   let MutableRectangle$ = dart.generic(function(T) {
     class MutableRectangle extends _RectangleBase$(T) {
       MutableRectangle(left, top, width, height) {
         this.left = left;
         this.top = top;
-        this._width = width['<'](0) ? _clampToZero(width) : width;
-        this._height = height['<'](0) ? _clampToZero(height) : height;
+        this._width = dart.as(width['<'](0) ? _clampToZero(width) : width, T);
+        this._height = dart.as(height['<'](0) ? _clampToZero(height) : height, T);
         super._RectangleBase();
       }
       MutableRectangle$fromPoints(a, b) {
         let left = dart.as(min(a.x, b.x), T);
         let width = dart.as(core.num['-'](max(a.x, b.x), left), T);
         let top = dart.as(min(a.y, b.y), T);
         let height = dart.as(core.num['-'](max(a.y, b.y), top), T);
         return new MutableRectangle(left, top, width, height);
       }
       get width() {
@@ skipping 45 matching lines @@
   math.exp = exp;
   math.log = log;
   math.Point = Point;
   math.Point$ = Point$;
   math.Random = Random;
   math.Rectangle = Rectangle;
   math.Rectangle$ = Rectangle$;
   math.MutableRectangle = MutableRectangle;
   math.MutableRectangle$ = MutableRectangle$;
 })(math || (math = {}));