Bug 502907 - Allow for the registration of cleanup functions that run when the harness is done

Consumers can now call do_register_cleanup with a function that will run when
the harness is done running the tests.
r=ted

testing/xpcshell/head.js

@@ -49,6 +49,7 @@ var _quit = false;
 var _passed = true;
 var _tests_pending = 0;
 var _passedChecks = 0, _falsePassedChecks = 0;
+var _cleanupFunctions = [];
 
 // Disable automatic network detection, so tests work correctly when
 // not connected to a network.
@@ -136,6 +137,11 @@ function _execute_test() {
   // _TAIL_FILES is dynamically defined by <runxpcshelltests.py>.
   _load_files(_TAIL_FILES);
 
+  // Execute all of our cleanup functions.
+  var func;
+  while ((func = _cleanupFunctions.pop()))
+    func();
+
   if (!_passed)
     return;
 
@@ -337,3 +343,15 @@ function do_parse_document(aPath, aType) {
   lf = null;
   return doc;
 }
+
+/**
+ * Registers a function that will run when the test harness is done running all
+ * tests.
+ *
+ * @param aFunction
+ *        The function to be called when the test harness has finished running.
+ */
+function do_register_cleanup(aFunction)
+{
+  _cleanupFunctions.push(aFunction);
+}