Implement CHA through type mask and TypedSelector in the simple type inferrer.

sdk/lib/_internal/compiler/implementation/world.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of dart2js;
 
 class World {
   final Compiler compiler;
   final Map<ClassElement, Set<MixinApplicationElement>> mixinUses;
   final Map<ClassElement, Set<ClassElement>> typesImplementedBySubclasses;
@@ skipping 143 matching lines @@
         mixinUses.putIfAbsent(mixin, () =>
                               new Set<MixinApplicationElement>());
     users.add(mixinApplication);
   }
 
   bool isUsedAsMixin(ClassElement cls) {
     Set<MixinApplicationElement> uses = mixinUses[cls];
     return uses != null && !uses.isEmpty;
   }
 
+  bool hasAnySubclass(ClassElement cls) {
+    Set<ClassElement> classes = subclasses[cls];
+    return classes != null && !classes.isEmpty;
+  }
+
+  bool hasAnySubtype(ClassElement cls) {
+    Set<ClassElement> classes = subtypes[cls];
+    return classes != null && !classes.isEmpty;
+  }
+
   void registerRtiDependency(Element element, Element dependency) {
     // We're not dealing with typedef for now.
     if (!element.isClass() || !dependency.isClass()) return;
     Set<ClassElement> classes =
         rtiDependencies.putIfAbsent(element, () => new Set<ClassElement>());
     classes.add(dependency);
   }
 
   bool needsRti(ClassElement cls) {
     return classesNeedingRti.contains(cls) || compiler.enabledRuntimeType;
@@ skipping 56 matching lines @@
     if (mask != null) {
       noSuchMethodSelector = new TypedSelector(mask, noSuchMethodSelector);
     }
     ClassElement objectClass = compiler.objectClass;
     return allFunctions
         .filter(noSuchMethodSelector)
         .map((Element member) => member.getEnclosingClass())
         .where((ClassElement holder) => !identical(holder, objectClass));
   }
 }