Introduce a helper to emit import script tags.

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.
 
 String emitCode(
       Compiler compiler,
       Unparser unparser,
       Map<LibraryElement, String> imports,
       Collection<Element> topLevelElements,
       Map<ClassElement, Collection<Element>> classMembers) {
   void outputElement(Element element) {
     unparser.unparse(element.parseNode(compiler));
   }
 
   void outputClass(ClassElement classElement, Collection<Element> members) {
     unparser.unparseClassWithBody(classElement.parseNode(compiler), () {
       members.forEach((element) {
         // TODO(smok): Filter out default constructors here.
         outputElement(element);
       });
     });
   }
 
   imports.forEach((libraryElement, prefix) {
-    unparser.addString('#import("${libraryElement.uri}",prefix:"$prefix");');
+    unparser.unparseImportTag('${libraryElement.uri}', prefix);
   });
 
   for (final element in topLevelElements) {
     if (element is ClassElement) {
       outputClass(element, classMembers[element]);
     } else {
       outputElement(element);
     }
   }
 }