dart2js cps: Fix return type for native functions.

pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
index 1f85d501be295579aa946beac49033195719e4b5..13dad911db2459e24afe96d032ac86ef93dcc0f4 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_nodes.dart
@@ -1529,12 +1529,12 @@ class CreateInvocationMirror extends Primitive {
 
 class ForeignCode extends UnsafePrimitive {
   final js.Template codeTemplate;
-  final TypeMask type;
+  final TypeMask storedType;

[asgerf, 2016/01/19 19:22:04]

This field clashed with the .type field inherited from Primitive. But since this
field is final any attempts to reassign it (in type propagation) would instead
change the inherited (un-readable) field from Primitive.

I will open an analyzer feature request to detect this kind of nonsense.

Apart from renaming the field, another solution would be to just never change
its type after initialization (which is essentially what happened before, but in
a very subtle way).

   final List<Reference<Primitive>> arguments;
   final native.NativeBehavior nativeBehavior;
   final FunctionElement dependency;
 
-  ForeignCode(this.codeTemplate, this.type, List<Primitive> arguments,
+  ForeignCode(this.codeTemplate, this.storedType, List<Primitive> arguments,
       this.nativeBehavior, {this.dependency})
       : this.arguments = _referenceList(arguments);