Add a new implementation of HashMap that uses JS objects for its (multiple) hash tables.

sdk/lib/_internal/libraries.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 libraries;
 
 /**
  * A bit flag used by [LibraryInfo] indicating that a library is used by dart2js
  */
 const int DART2JS_PLATFORM = 1;
@@ skipping 12 matching lines @@
 const Map<String, LibraryInfo> LIBRARIES = const {
 
   "async": const LibraryInfo(
       "async/async.dart",
       dart2jsPatchPath: "_internal/compiler/implementation/lib/async_patch.dart"),
 
   "chrome": const LibraryInfo(
       "chrome/dart2js/chrome_dart2js.dart",
       category: "Client"),
 
-  "collection": const LibraryInfo("collection/collection.dart"),
+  "collection": const LibraryInfo(
+      "collection/collection.dart",
+      dart2jsPatchPath: "_internal/compiler/implementation/lib/collection_patch.dart"),
 
   "core": const LibraryInfo(
       "core/core.dart",
       dart2jsPatchPath: "_internal/compiler/implementation/lib/core_patch.dart"),
 
   "crypto": const LibraryInfo(
       "crypto/crypto.dart"),
 
   "html": const LibraryInfo(
       "html/dartium/html_dartium.dart",
@@ skipping 155 matching lines @@
                     this.category: "Shared",
                     this.dart2jsPath,
                     this.dart2jsPatchPath,
                     this.implementation: false,
                     this.documented: true,
                     this.platforms: DART2JS_PLATFORM | VM_PLATFORM});
 
   bool get isDart2jsLibrary => (platforms & DART2JS_PLATFORM) != 0;
   bool get isVmLibrary => (platforms & VM_PLATFORM) != 0;
 }