dart2js cps_ir: Use interceptors for is-checks (version 2)

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

Index: pkg/compiler/lib/src/cps_ir/type_mask_system.dart
diff --git a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
index a84d28d4ba5cd333e83868f839722da0da625407..3aec705a3e92ba20274418fe7ad46815f27db35b 100644
--- a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
@@ -42,6 +42,7 @@ class TypeMaskSystem {
   TypeMask get extendableNativeListType => backend.extendableArrayType;
 
   TypeMask numStringBoolType;
+  TypeMask interceptorType;
 
   ClassElement get jsNullClass => backend.jsNullClass;
 
@@ -63,6 +64,9 @@ class TypeMaskSystem {
     numStringBoolType =
         new TypeMask.unionOf(<TypeMask>[anyNum, anyString, anyBool],
             classWorld);
+
+    interceptorType = new TypeMask.nonNullSubtype(

[Kevin Millikin (Google), 2015/10/07 14:10:49]

I guess all the lines above are broken like

interceptorType =
    new TypeMask.nonNullSubtype(backend.jsInterceptorClass, classWorld);

which I think looks a bit better (broken at a lower precedence operator, avoids
the unsightly dangling left paren).

[sra1, 2015/10/07 17:45:58]

Done.

+        backend.jsInterceptorClass, classWorld);
   }
 
   bool methodUsesReceiverArgument(FunctionElement function) {
@@ -199,6 +203,9 @@ class TypeMaskSystem {
     return t.satisfies(backend.jsIntClass, classWorld);
   }
 
+  // TODO(sra): Find a better name.  'NativeList' is a bad name because there
+  // are many native classes in dart:html that implement List but are not (and
+  // should not be) included in this predicate.
   bool isDefinitelyNativeList(TypeMask t, {bool allowNull: false}) {
     if (!allowNull && t.isNullable) return false;
     return t.nonNullable().satisfies(backend.jsArrayClass, classWorld);