Allow using native JS []= on typed data lists.

sdk/lib/_internal/compiler/implementation/js_backend/backend.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 js_backend;
 
 typedef void Recompile(Element element);
 
 class ReturnInfo {
   HType returnType;
@@ skipping 634 matching lines @@
   ClassElement jsStringClass;
   ClassElement jsArrayClass;
   ClassElement jsNumberClass;
   ClassElement jsIntClass;
   ClassElement jsDoubleClass;
   ClassElement jsFunctionClass;
   ClassElement jsNullClass;
   ClassElement jsBoolClass;
 
   ClassElement jsIndexableClass;
+  ClassElement jsMutableIndexableClass;
+
   ClassElement jsMutableArrayClass;
   ClassElement jsFixedArrayClass;
   ClassElement jsExtendableArrayClass;
 
   Element jsIndexableLength;
   Element jsArrayRemoveLast;
   Element jsArrayAdd;
   Element jsStringSplit;
   Element jsStringConcat;
   Element jsStringToString;
@@ skipping 226 matching lines @@
       jsBoolClass = compiler.findInterceptor(const SourceString('JSBool')),
       jsMutableArrayClass =
           compiler.findInterceptor(const SourceString('JSMutableArray')),
       jsFixedArrayClass =
           compiler.findInterceptor(const SourceString('JSFixedArray')),
       jsExtendableArrayClass =
           compiler.findInterceptor(const SourceString('JSExtendableArray'))];
 
     jsIndexableClass =
         compiler.findInterceptor(const SourceString('JSIndexable'));
+    jsMutableIndexableClass =
+        compiler.findInterceptor(const SourceString('JSMutableIndexable'));
 
     // TODO(kasperl): Some tests do not define the special JSArray
     // subclasses, so we check to see if they are defined before
     // trying to resolve them.
     if (jsFixedArrayClass != null) {
       jsFixedArrayClass.ensureResolved(compiler);
     }
     if (jsExtendableArrayClass != null) {
       jsExtendableArrayClass.ensureResolved(compiler);
     }
@@ skipping 864 matching lines @@
   ClassElement get constListImplementation => jsArrayClass;
   ClassElement get fixedListImplementation => jsFixedArrayClass;
   ClassElement get growableListImplementation => jsExtendableArrayClass;
   ClassElement get mapImplementation => mapLiteralClass;
   ClassElement get constMapImplementation => constMapLiteralClass;
   ClassElement get functionImplementation => jsFunctionClass;
   ClassElement get typeImplementation => typeLiteralClass;
   ClassElement get boolImplementation => jsBoolClass;
   ClassElement get nullImplementation => jsNullClass;
 }