Typecheck constructor initializers properly

test/codegen/expect/core/core.js

Index: test/codegen/expect/core/core.js
diff --git a/test/codegen/expect/core/core.js b/test/codegen/expect/core/core.js
index ab011bd37149982f30e1f539ab8bf37612ace304..8f6fa837529f7c7e6145ce6f7f156a316b25f0c9 100644
--- a/test/codegen/expect/core/core.js
+++ b/test/codegen/expect/core/core.js
@@ -255,12 +255,12 @@ var core;
       return new Duration({milliseconds: ms - otherMs});
     }
     DateTime$_internal(year, month, day, hour, minute, second, millisecond, isUtc) {
-      this.isUtc = typeof isUtc == boolean ? isUtc : dart.throw_(new ArgumentError(isUtc));
-      this.millisecondsSinceEpoch = dart.dinvokef(/* Unimplemented unknown name */checkInt, dart.dinvoke(/* Unimplemented unknown name */Primitives, 'valueFromDecomposedDate', year, month, day, hour, minute, second, millisecond, isUtc));
+      this.isUtc = dart.as(typeof isUtc == boolean ? isUtc : dart.throw_(new ArgumentError(isUtc)), bool);
+      this.millisecondsSinceEpoch = dart.as(dart.dinvokef(/* Unimplemented unknown name */checkInt, dart.dinvoke(/* Unimplemented unknown name */Primitives, 'valueFromDecomposedDate', year, month, day, hour, minute, second, millisecond, isUtc)), int);
     }
     DateTime$_now() {
       this.isUtc = false;
-      this.millisecondsSinceEpoch = dart.dinvoke(/* Unimplemented unknown name */Primitives, 'dateNow');
+      this.millisecondsSinceEpoch = dart.as(dart.dinvoke(/* Unimplemented unknown name */Primitives, 'dateNow'), int);
     }
     static _brokenDownDateToMillisecondsSinceEpoch(year, month, day, hour, minute, second, millisecond, isUtc) {
       return dart.as(dart.dinvoke(/* Unimplemented unknown name */Primitives, 'valueFromDecomposedDate', year, month, day, hour, minute, second, millisecond, isUtc), int);
@@ -649,7 +649,7 @@ var core;
       if (length === void 0)
         length = null;
       this.indexable = indexable;
-      this.length = length !== null ? length : dart.dload(indexable, 'length');
+      this.length = dart.as(length !== null ? length : dart.dload(indexable, 'length'), int);
       super.ArgumentError$value(invalidValue, name, message !== null ? message : "Index out of range");
     }
     get start() {
@@ -1032,7 +1032,7 @@ var core;
       _GeneratorIterable(_end, generator) {
         this._end = _end;
         this._start = 0;
-        this._generator = generator !== null ? generator : _id;
+        this._generator = dart.as(generator !== null ? generator : _id, _Generator);
         super.IterableBase();
       }
       _GeneratorIterable$slice(_start, _end, _generator) {