add checks needed for covariant generics, and List<E>

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 b167cdec406e5d50f9df2dddbcf09536f6d8b1c8..216bc5e3716a77a9aab1f501c299afdc9feadc7b 100644
--- a/lib/runtime/dart/math.js
+++ b/lib/runtime/dart/math.js
@@ -22,6 +22,8 @@ var math;
   let Point$ = dart.generic(function(T) {
     class Point extends core.Object {
       Point(x, y) {
+        dart.as(x, T);
+        dart.as(y, T);
         this.x = x;
         this.y = y;
       }
@@ -137,6 +139,10 @@ var math;
   let Rectangle$ = dart.generic(function(T) {
     class Rectangle extends _RectangleBase$(T) {
       Rectangle(left, top, width, height) {
+        dart.as(left, T);
+        dart.as(top, T);
+        dart.as(width, T);
+        dart.as(height, T);
         this.left = left;
         this.top = top;
         this.width = dart.as(width['<'](0) ? dart.notNull(width['unary-']()) * 0 : width, T);
@@ -160,6 +166,10 @@ var math;
   let MutableRectangle$ = dart.generic(function(T) {
     class MutableRectangle extends _RectangleBase$(T) {
       MutableRectangle(left, top, width, height) {
+        dart.as(left, T);
+        dart.as(top, T);
+        dart.as(width, T);
+        dart.as(height, T);
         this.left = left;
         this.top = top;
         this[_width] = dart.as(width['<'](0) ? _clampToZero(width) : width, T);
@@ -177,6 +187,7 @@ var math;
         return this[_width];
       }
       set width(width) {
+        dart.as(width, T);
         if (width['<'](0))
           width = dart.as(_clampToZero(width), T);
         this[_width] = width;
@@ -185,6 +196,7 @@ var math;
         return this[_height];
       }
       set height(height) {
+        dart.as(height, T);
         if (height['<'](0))
           height = dart.as(_clampToZero(height), T);
         this[_height] = height;