Fork test scripts to support special runtime checkout.

testing/dart/multitest.dart

Index: testing/dart/multitest.dart
===================================================================
--- testing/dart/multitest.dart	(revision 1975)
+++ testing/dart/multitest.dart	(working copy)
@@ -188,15 +188,13 @@
   if (!parent_dir.existsSync()) {
     parent_dir.createSync();
   }
-  final String prefix = 'tests/';
-  final String suffix = '/src';
-  Expect.isTrue(testDir.startsWith(prefix));
-  Expect.isTrue(testDir.endsWith(suffix));
-  String path = parent_dir.path +
-      testDir.substring(prefix.length, testDir.length - suffix.length);
+  var split = testDir.split(new Platform().pathSeparator());
+  var lastComponent = split.removeLast();
+  Expect.isTrue(lastComponent == 'src');
+  String path = parent_dir.path + split.last();
   Directory dir = new Directory(path);
   if (!dir.existsSync()) {
     dir.createSync();
   }
   return path;
-}
+}