dart2js cps: More interceptor optimizations and fixes.

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 6910d46392df3b18538939d2143c30cd88b22459..9c46857f443c731f93226c45914f329cf3dc4bb5 100644
--- a/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
+++ b/pkg/compiler/lib/src/cps_ir/type_mask_system.dart
@@ -45,6 +45,7 @@ class TypeMaskSystem {
   TypeMask numStringBoolType;
   TypeMask fixedLengthType;
   TypeMask interceptorType;
+  TypeMask interceptedTypes; // Does not include null.
 
   TypeMask _indexableTypeTest;
 
@@ -71,6 +72,12 @@ class TypeMaskSystem {
     interceptorType =
         new TypeMask.nonNullSubtype(backend.jsInterceptorClass, classWorld);
 
+    // We redundantly include subtypes of num/string/bool as intercepted types,
+    // because the type system does not infer that their implementations are
+    // all subclasses of Interceptor.
+    interceptedTypes = new TypeMask.unionOf(
+        <TypeMask>[interceptorType, numStringBoolType], classWorld);
+
     TypeMask typedArray = nonNullSubclass(backend.typedArrayClass);
     fixedLengthType = new TypeMask.unionOf(
         <TypeMask>[stringType, backend.fixedArrayType, typedArray],
@@ -281,6 +288,24 @@ class TypeMaskSystem {
     return fixedLengthType.containsMask(t.nonNullable(), classWorld);
   }
 
+  bool isDefinitelyIntercepted(TypeMask t, {bool allowNull}) {
+    assert(allowNull != null);
+    if (!allowNull && t.isNullable) return false;
+    return interceptedTypes.containsMask(t.nonNullable(), classWorld);
+  }
+
+  /// Given a class from the interceptor hierarchy, returns a [TypeMask]
+  /// matching all values with that interceptor (or a subtype thereof).
+  TypeMask getInterceptorSubtypes(ClassElement class_) {
+    if (class_ == backend.jsInterceptorClass) {
+      return interceptorType.nullable();
+    } else if (class_ == backend.jsNullClass) {
+      return nullType;
+    } else {
+      return nonNullSubclass(class_);
+    }
+  }
+
   bool areDisjoint(TypeMask leftType, TypeMask rightType) {
     TypeMask intersection = leftType.intersection(rightType, classWorld);
     return intersection.isEmpty && !intersection.isNullable;