Introduce a helper to emit import script tags.

lib/compiler/implementation/tree/unparser.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.
 
 // Returns null if no need to rename a node.
 typedef String Renamer(Node node);
 
 String unparse(Node node) {
   Unparser unparser = new Unparser();
   unparser.unparse(node);
   return unparser.result;
 }
 
 class Unparser implements Visitor {
   Renamer rename;
   final StringBuffer sb;
 
   String get result => sb.toString();
 
   Unparser() : sb = new StringBuffer() {
     // TODO(smok): Move this to initializer once dart2js stops complaining
     // about closures in initializers.
     rename = (Node node) => null;
   }
   Unparser.withRenamer(this.rename) : sb = new StringBuffer();
 
-  // TODO(antonm): will go away soon.
-  void addString(String s) {
-    sb.add(s);
-  }
-
   void add(SourceString string) {
     string.printOn(sb);
   }
 
   void addToken(Token token) {
     if (token === null) return;
     add(token.value);
     if (token.kind === KEYWORD_TOKEN || token.kind === IDENTIFIER_TOKEN) {
       sb.add(' ');
     }
@@ skipping 419 matching lines @@
   }
 
   visitSwitchCase(SwitchCase node) {
     visit(node.labelsAndCases);
     if (node.isDefaultCase) {
       sb.add('default:');
     }
     visit(node.statements);
   }
 
+  unparseImportTag(String uri, [String prefix]) {
+    final suffix = prefix === null ? '' : ',prefix:"$prefix"';
+    sb.add('#import("$uri"$suffix);');
+  }
+
   visitScriptTag(ScriptTag node) {
     add(node.beginToken.value);
     visit(node.tag);
     sb.add('(');
     visit(node.argument);
     if (node.prefixIdentifier !== null) {
       visit(node.prefixIdentifier);
       sb.add(':');
       visit(node.prefix);
     }
@@ skipping 36 matching lines @@
       sb.add(' ');
     }
     visit(node.name);
     if (node.typeParameters !== null) {
       visit(node.typeParameters);
     }
     visit(node.formals);
     add(node.endToken.value);
   }
 }