sdk files reorganization to make dart2js a proper package

sdk/lib/_internal/js_runtime/lib/collection_patch.dart

 // Copyright (c) 2013, 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.
 
 // Patch file for dart:collection classes.
 import 'dart:_foreign_helper' show JS;
 import 'dart:_js_helper' show
     fillLiteralMap, InternalMap, NoInline, NoSideEffects, NoThrows, patch,
     JsLinkedHashMap, LinkedHashMapCell, LinkedHashMapKeyIterable,
     LinkedHashMapKeyIterator;
@@ skipping 1637 matching lines @@
     } else if (_cell == null) {
       _current = null;
       return false;
     } else {
       _current = _cell._element;
       _cell = _cell._next;
       return true;
     }
   }
 }