Add an exception for a flakey error in DirectoryWatcherTest...

base/data/purify/base_unittests.exe_MLK_flakey.txt

Index: base/data/purify/base_unittests.exe_MLK_flakey.txt
===================================================================
--- base/data/purify/base_unittests.exe_MLK_flakey.txt	(revision 9313)
+++ base/data/purify/base_unittests.exe_MLK_flakey.txt	(working copy)
@@ -6,3 +6,13 @@
    base/wmi_util_unittest.cc  WMIUtilTest_TestLaunchProcess_Test::TestBody(void)
    testing/gtest/src/gtest.cc  testing::Test::Run(void)
    ^^^  
+
+base::ObjectWatcher::StartWatching(void *,Delegate::ObjectWatcher::base *) [base_unittests.exe]
+Alloc Location
+   ...  
+   base/object_watcher.cc  base::ObjectWatcher::StartWatching(void *,Delegate::ObjectWatcher::base *)
+   base/directory_watcher_win.cc  DirectoryWatcher::Impl::OnObjectSignaled(void *)
+   base/object_watcher.cc  base::ObjectWatcher::Watch::Run(void)
+   base/message_loop.cc  MessageLoop::RunTask(Task *)
+   ^^^  
+