Move some core classes to collection library.

sdk/lib/_internal/compiler/implementation/mirrors/dart2js_mirror.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 mirrors_dart2js;
 
 import 'dart:async';
+import 'dart:collection' show LinkedHashMap;
 import 'dart:io';
 import 'dart:uri';
 
 import '../../compiler.dart' as diagnostics;
 import '../elements/elements.dart';
 import '../resolution/resolution.dart' show ResolverTask, ResolverVisitor;
 import '../apiimpl.dart' as api;
 import '../scanner/scannerlib.dart' hide SourceString;
 import '../ssa/ssa.dart';
 import '../dart2jslib.dart';
@@ skipping 1841 matching lines @@
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, text));
     } else if (fieldName == 'trimmedText') {
       return new Future.immediate(
           new Dart2JsStringConstantMirror.fromString(mirrors, trimmedText));
     }
     // TODO(johnniwinther): Which exception/error should be thrown here?
     throw new UnsupportedError('InstanceMirror does not have a reflectee');
   }
 }