Clean-up of getCompilationUnit.

lib/compiler/implementation/js/nodes.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.
 
 interface NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
   T visitExpressionStatement(ExpressionStatement node);
   T visitEmptyStatement(EmptyStatement node);
@@ skipping 539 matching lines @@
 class New extends Call {
   New(Expression cls, List<Expression> arguments) : super(cls, arguments);
 
   accept(NodeVisitor visitor) => visitor.visitNew(this);
 }
 
 class Binary extends Call {
   Binary(String op, Expression left, Expression right)
       : super(new VariableUse(op), <Expression>[left, right]);
 
-  String get op() => (target as VariableUse).name;
+  String get op() {
+    VariableUse use = target;
+    return use.name;
+  }
+
   Expression get left() => arguments[0];
   Expression get right() => arguments[1];
 
   accept(NodeVisitor visitor) => visitor.visitBinary(this);
 
   int get precedenceLevel() {
     // TODO(floitsch): switch to constant map.
     switch (op) {
       case "*":
       case "/":
@@ skipping 253 matching lines @@
   /** Contains the pattern and the flags.*/
   String pattern;
 
   RegExpLiteral(this.pattern);
 
   accept(NodeVisitor visitor) => visitor.visitRegExpLiteral(this);
   void visitChildren(NodeVisitor visitor) {}
 
   int get precedenceLevel() => PRIMARY;
 }