Add support for client/dartc compilation only tests.

runtime/bin/directory.dart

Index: runtime/bin/directory.dart
diff --git a/runtime/bin/directory.dart b/runtime/bin/directory.dart
index b98fd45297c3124c0b144f93c00b03bca9ee5f30..222b3de471b3ebd5ca60ca1ca5cc8b2a5e115a78 100644
--- a/runtime/bin/directory.dart
+++ b/runtime/bin/directory.dart
@@ -35,6 +35,16 @@ interface Directory factory _Directory {
   void createTemp();
 
   /**
+   * Synchronously creates a temporary directory with a name based on the current path.
+   * This name and path is used as a template, and additional characters are
+   * appended to it by the call to make a unique directory name.  If the
+   * path is the empty string, a default system temp directory and name
+   * are used for the template.
+   * The path is modified to be the path of the new directory.
+   */
+  void createTempSync();
+
+  /**
    * Deletes the directory with this name. Throws an exception
    * if the directory is not empty or if deletion failed.
    */