Add test for native extensions that copies the extension to a test directory and runs it.

tools/testing/dart/multitest.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.
 
 #library("multitest");
 
 #import("dart:io");
 #import("test_suite.dart");
 
 // Multitests are Dart test scripts containing lines of the form
@@ skipping 142 matching lines @@
 // Find all relative imports and copy them into the dir that contains
 // the generated tests.
 Set<String> _findAllRelativeImports(String topLibrary) {
   Set<String> toSearch = new Set<String>.from([topLibrary]);
   Set<String> foundImports = new HashSet<String>();
   String pathSep = Platform.pathSeparator;
   int end = topLibrary.lastIndexOf(pathSep);
   String libraryDir = topLibrary.substring(0, end);
 
   // Matches #import( or #source( followed by " or ' followed by anything
-  // except dart: or /, at the beginning of a line.
-  RegExp relativeImportRegExp =
-      const RegExp('^#(import|source)[(]["\'](?!(dart:|/))([^"\']*)["\']');
+  // except dart:, dart-ext: or /, at the beginning of a line.
+  RegExp relativeImportRegExp = const RegExp(
+      '^#(import|source)[(]["\'](?!(dart:|dart-ext:|/))([^"\']*)["\']');
   while (!toSearch.isEmpty()) {
     var thisPass = toSearch;
     toSearch = new HashSet<String>();
     for (String filename in thisPass) {
       File f = new File(filename);
       for (String line in f.readAsLinesSync()) {
         Match match = relativeImportRegExp.firstMatch(line);
         if (match != null) {
           String relativePath = match.group(3);
           if (foundImports.contains(relativePath)) {
@@ skipping 92 matching lines @@
     // TestSuite.forDirectory.
     split.removeLast();
   }
   String path = '${generatedTestDir.path}/${split.last()}';
   Directory dir = new Directory(path);
   if (!dir.existsSync()) {
     dir.createSync();
   }
   return path;
 }