merge class extensions from patch files

test/codegen/expect/collection/collection.js

 var collection;
 (function(collection) {
   'use strict';
   let _HashMap$ = dart.generic(function(K, V) {
     class _HashMap extends dart.Object {
       _HashMap() {
         this._length = 0;
         this._strings = null;
         this._nums = null;
         this._rest = null;
@@ skipping 2254 matching lines @@
         let value = opt$.value === void 0 ? null : opt$.value;
         let map = new LinkedHashMap();
         Maps._fillMapWithMappedIterable(map, iterable, key, value);
         return map;
       }
       LinkedHashMap$fromIterables(keys, values) {
         let map = new LinkedHashMap();
         Maps._fillMapWithIterables(map, keys, values);
         return map;
       }
+      LinkedHashMap$_literal(keyValuePairs) {
+        return dart.as(dart.dinvokef(/* Unimplemented unknown name */fillLiteralMap, keyValuePairs, new _LinkedHashMap()), LinkedHashMap$(K, V));
+      }
+      LinkedHashMap$_empty() {
+        return new _LinkedHashMap();
+      }
     }
     dart.defineNamedConstructor(LinkedHashMap, 'identity');
     dart.defineNamedConstructor(LinkedHashMap, 'from');
     dart.defineNamedConstructor(LinkedHashMap, 'fromIterable');
     dart.defineNamedConstructor(LinkedHashMap, 'fromIterables');
+    dart.defineNamedConstructor(LinkedHashMap, '_literal');
+    dart.defineNamedConstructor(LinkedHashMap, '_empty');
     return LinkedHashMap;
   });
   let LinkedHashMap = LinkedHashMap$(dynamic, dynamic);
   let LinkedHashSet$ = dart.generic(function(E) {
     class LinkedHashSet extends dart.Object {
       LinkedHashSet(opt$) {
         let equals = opt$.equals === void 0 ? null : opt$.equals;
         let hashCode = opt$.hashCode === void 0 ? null : opt$.hashCode;
         let isValidKey = opt$.isValidKey === void 0 ? null : opt$.isValidKey;
         if (isValidKey === null) {
@@ skipping 2489 matching lines @@
   collection.ListQueue$ = ListQueue$;
   collection.SetMixin = SetMixin;
   collection.SetMixin$ = SetMixin$;
   collection.SetBase = SetBase;
   collection.SetBase$ = SetBase$;
   collection.SplayTreeMap = SplayTreeMap;
   collection.SplayTreeMap$ = SplayTreeMap$;
   collection.SplayTreeSet = SplayTreeSet;
   collection.SplayTreeSet$ = SplayTreeSet$;
 })(collection || (collection = {}));