Implement optimized mixin application in dart2js

pkg/compiler/lib/src/elements/modelx.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.
 
 library elements.modelx;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers;
 import '../common/resolution.dart' show Resolution, ParsingContext;
 import '../compiler.dart' show Compiler;
@@ skipping 1056 matching lines @@
    * library is loaded.
    */
   Link<Element> slotForExports;
 
   List<ImportElement> _imports = <ImportElement>[];
   List<ExportElement> _exports = <ExportElement>[];
 
   final Map<LibraryDependency, LibraryElement> tagMapping =
       new Map<LibraryDependency, LibraryElement>();
 
+  final Map<String, MixinApplicationElementX> mixinApplicationCache =
+      <String, MixinApplicationElementX>{};
+
   LibraryElementX(Script script, [Uri canonicalUri, LibraryElementX origin])
       : this.canonicalUri =
             ((canonicalUri == null) ? script.readableUri : canonicalUri),
         this.isSynthesized = script.isSynthesized,
         super(script.name, ElementKind.LIBRARY, null) {
     entryCompilationUnit = new CompilationUnitElementX(script, this);
     if (origin != null) {
       origin.applyPatch(this);
     }
   }
@@ skipping 2514 matching lines @@
       body = node.asFunctionExpression().body;
     }
     return new ParsedResolvedAst(
         declaration,
         node,
         body,
         definingElement.treeElements,
         definingElement.compilationUnit.script.resourceUri);
   }
 }