restore arrow function bind this workaround

lib/src/codegen/js_codegen.dart

 // Copyright (c) 2015, 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 dev_compiler.src.codegen.js_codegen;
 
 import 'dart:collection' show HashSet, HashMap, SplayTreeSet;
 
 import 'package:analyzer/analyzer.dart' hide ConstantEvaluator;
 import 'package:analyzer/src/generated/ast.dart' hide ConstantEvaluator;
@@ skipping 1271 matching lines @@
 
   @override
   JS.Statement visitFunctionDeclarationStatement(
       FunctionDeclarationStatement node) {
     var func = node.functionDeclaration;
     if (func.isGetter || func.isSetter) {
       return js.comment('Unimplemented function get/set statement: $node');
     }
 
     var fn = _visit(func.functionExpression);
-    var jsThis = new _JsThisFinder();
-    fn.accept(jsThis);
 
     var name = new JS.Identifier(func.name.name);
     JS.Statement declareFn;
-    if (jsThis.found) {
+    if (JS.This.foundIn(fn)) {
       declareFn = js.statement('let # = #.bind(this);', [name, fn]);
     } else {
       declareFn = new JS.FunctionDeclaration(name, fn);
     }
 
     return new JS.Block([
       declareFn,
       _emitFunctionTagged(name, func.element.type).toStatement()
     ]);
   }
@@ skipping 1509 matching lines @@
 
   String generateLibrary(LibraryUnit unit) {
     // Clone the AST first, so we can mutate it.
     unit = unit.clone();
     var library = unit.library.element.library;
     var fields = findFieldsNeedingStorage(unit);
     var codegen =
         new JSCodegenVisitor(compiler, library, _extensionTypes, fields);
     var module = codegen.emitLibrary(unit);
     var out = compiler.getOutputPath(library.source.uri);
-    return writeJsLibrary(module, out, emitSourceMaps: options.emitSourceMaps);
+    return writeJsLibrary(module, out,
+        emitSourceMaps: options.emitSourceMaps,
+        arrowFnBindThisWorkaround: options.arrowFnBindThisWorkaround);
   }
 }
 
 /// Choose a canonical name from the library element.
 /// This never uses the library's name (the identifier in the `library`
 /// declaration) as it doesn't have any meaningful rules enforced.
 String jsLibraryName(LibraryElement library) => canonicalLibraryName(library);
 
 /// Shorthand for identifier-like property names.
 /// For now, we emit them as strings and the printer restores them to
@@ skipping 14 matching lines @@
 
 /// A special kind of element created by the compiler, signifying a temporary
 /// variable. These objects use instance equality, and should be shared
 /// everywhere in the tree where they are treated as the same variable.
 class TemporaryVariableElement extends LocalVariableElementImpl {
   TemporaryVariableElement.forNode(Identifier name) : super.forNode(name);
 
   int get hashCode => identityHashCode(this);
   bool operator ==(Object other) => identical(this, other);
 }
-
-class _JsThisFinder extends JS.BaseVisitor {
-  bool found = false;
-  visitThis(JS.This node) {
-    found = true;
-  }
-  visitNode(JS.Node node) {
-    if (!found) super.visitNode(node);
-  }
-}