Fix intermittent DCHECK failure in BlacklistManagerTest.

chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc

Index: chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc
diff --git a/chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc b/chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc
index 51814e75d746b97345f1c5026fd0b59bdfea7e73..f4323819e30d61ada85bbcb51fa429293edabbf8 100644
--- a/chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc
+++ b/chrome/browser/privacy_blacklist/blacklist_manager_unittest.cc
@@ -96,6 +96,7 @@ class BlacklistManagerTest : public testing::Test, public NotificationObserver {
   }
 
   virtual void TearDown() {
+    mock_file_thread_.Stop();
     loop_.RunAllPending();
   }