Fix some errors around []= in core types.

pkg/dev_compiler/tool/input_sdk/private/js_array.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 dart._interceptors;
 
 /**
  * The interceptor class for [List]. The compiler recognizes this
  * class as an interceptor, and changes references to [:this:] to
  * actually use the receiver of the method, which is generated as an extra
  * argument added to each member.
  */
 @JsPeerInterface(name: 'Array')
-class JSArray<E> implements List<E>, JSIndexable {
+class JSArray<E> implements List<E>, JSIndexable<E> {
 
   const JSArray();
 
   /**
    * Constructor for adding type parameters to an existing JavaScript Array.
    */
   factory JSArray.typed(allocation) =>
       // TODO(jmesserly): skip this when E is dynamic and Object.
       JS('-dynamic', 'dart.list(#, #)', allocation, E);
 
@@ skipping 555 matching lines @@
  * Dummy subclasses that allow the backend to track more precise
  * information about arrays through their type. The CPA type inference
  * relies on the fact that these classes do not override [] nor []=.
  *
  * These classes are really a fiction, and can have no methods, since
  * getInterceptor always returns JSArray.  We should consider pushing the
  * 'isGrowable' and 'isMutable' checks into the getInterceptor implementation so
  * these classes can have specialized implementations. Doing so will challenge
  * many assuptions in the JS backend.
  */
-class JSMutableArray<E> extends JSArray<E> implements JSMutableIndexable {}
+class JSMutableArray<E> extends JSArray<E> {}
 class JSFixedArray<E> extends JSMutableArray<E> {}
 class JSExtendableArray<E> extends JSMutableArray<E> {}
 class JSUnmodifiableArray<E> extends JSArray<E> {} // Already is JSIndexable.
 
 
 /// An [Iterator] that iterates a JSArray.
 ///
 class ArrayIterator<E> implements Iterator<E> {
   final JSArray<E> _iterable;
   final int _length;
@@ skipping 17 matching lines @@
 
     if (_index >= length) {
       _current = null;
       return false;
     }
     _current = _iterable[_index];
     _index++;
     return true;
   }
 }