Fix resynthesis of operator[]= from summary.

pkg/analyzer/lib/src/summary/resynthesize.dart

 // Copyright (c) 2015, 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 summary_resynthesizer;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/element_handle.dart';
 import 'package:analyzer/src/generated/engine.dart';
@@ skipping 374 matching lines @@
   /**
    * Resynthesize an [ExecutableElement] and place it in the given [holder].
    */
   void buildExecutable(UnlinkedExecutable serializedExecutable,
       [ElementHolder holder]) {
     bool isTopLevel = holder == null;
     if (holder == null) {
       holder = unitHolder;
     }
     String name = serializedExecutable.name;
-    if (name.endsWith('=')) {
+    if (name.endsWith('=') && name != '[]=') {
       name = name.substring(0, name.length - 1);
     }
     UnlinkedExecutableKind kind = serializedExecutable.kind;
     switch (kind) {
       case UnlinkedExecutableKind.functionOrMethod:
         if (isTopLevel) {
           FunctionElementImpl executableElement =
               new FunctionElementImpl(name, -1);
           buildExecutableCommonParts(executableElement, serializedExecutable);
           holder.addFunction(executableElement);
@@ skipping 527 matching lines @@
       elementMap[cls.name] = cls;
     }
     for (FunctionTypeAliasElement typeAlias in unit.functionTypeAliases) {
       elementMap[typeAlias.name] = typeAlias;
     }
     resummarizedElements[absoluteUri] = elementMap;
     unitHolder = null;
     prelinkedUnit = null;
   }
 }