Clean-up of getCompilationUnit.

lib/compiler/implementation/dart_backend/emitter.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.
 
 /**
  * Dart backend helper for converting program IR back to source code.
  */
 class Emitter {
 
   final Compiler compiler;
@@ skipping 48 matching lines @@
     Unparser unparser = new Unparser.withRenamer(renamer.rename);
     // TODO(smok): Figure out why AbstractFieldElement appears here,
     // we have used getters/setters resolved instead of it.
     if (element is SynthesizedConstructorElement
         || element is AbstractFieldElement) return;
     if (element.isField()) {
       assert(element is VariableElement);
       // Different VariableElement's may refer to the same VariableListElement.
       // Output this list only once.
       // TODO: only emit used variables.
-      final variableList = (element as VariableElement).variables;
+      VariableElement variableElement = element;
+      final variableList = variableElement.variables;
       if (!processedVariableLists.contains(variableList)) {
         processedVariableLists.add(variableList);
         sb.add(unparser.unparse(variableList.parseNode(compiler)));
       }
     } else {
       sb.add(unparser.unparse(element.parseNode(compiler)));
     }
   }
 
   String toString() {
     final result = new StringBuffer();
     final libraries = compiler.libraries;
     for (final uri in libraries.getKeys()) {
       // Same library element may be a value for different uris as of now
       // e.g., core libraryElement is a value for both keys 'dart:core'
       // and full file name.  Only care about uris with dart scheme.
       if (!uri.startsWith('dart:')) continue;
       final lib = libraries[uri];
       if (renamer.imports.containsKey(lib)) {
         result.add('#import("$uri", prefix: "${renamer.imports[lib]}");');
       }
     }
     result.add(sb);
     return result.toString();
   }
 }