Start using the new union/intersection code for HType.INDEXABLE_PRIMITIVE.

tests/compiler/dart2js/mock_compiler.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.
 
 library mock_compiler;
 
 import 'dart:collection';
 import 'dart:uri';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
@@ skipping 45 matching lines @@
   class Dynamic_ {}
   class LinkedHashMap {}
   S() {}
   unwrapException(e) {}
   assertHelper(a){}
   createRuntimeType(a) {}
   throwNoSuchMethod(obj, name, arguments, expectedArgumentNames) {}
   throwAbstractClassInstantiationError(className) {}''';
 
 const String DEFAULT_INTERCEPTORSLIB = r'''
-  class JSArray implements List {
+  class JSIndexable {}
+  class JSArray implements List, JSIndexable {
     var length;
     operator[](index) {}
     operator[]=(index, value) {}
     var add;
   }
-  class JSString implements String {
+  class JSString implements String, JSIndexable {
     var length;
     operator[](index) {}
     toString() {}
   }
   class JSNumber implements num {
     // All these methods return a number to please type inferencing.
     operator-() => (this is JSInt) ? 42 : 42.0;
     operator +(other) => (this is JSInt) ? 42 : 42.0;
     operator -(other) => (this is JSInt) ? 42 : 42.0;
     operator ~/(other) => 42;
@@ skipping 281 matching lines @@
   }
 }
 
 class MockDeferredLoadTask extends DeferredLoadTask {
   MockDeferredLoadTask(Compiler compiler) : super(compiler);
 
   void registerMainApp(LibraryElement mainApp) {
     // Do nothing.
   }
 }