Fix shutdown crash in CertVerifier by using a MessageLoopProxy.

base/message_loop_proxy.h

Index: base/message_loop_proxy.h
diff --git a/base/message_loop_proxy.h b/base/message_loop_proxy.h
index 4d38155ec7435d2331c81778eff8ad600171b78a..6a8cbe8863623ab8bfd67cf12d603c15207ec751 100644
--- a/base/message_loop_proxy.h
+++ b/base/message_loop_proxy.h
@@ -16,7 +16,8 @@ struct MessageLoopProxyTraits;
 
 // This class provides a thread-safe refcounted interface to the Post* methods
 // of a message loop. This class can outlive the target message loop. You can
-// obtain a MessageLoopProxy via Thread::message_loop_proxy().
+// obtain a MessageLoopProxy via Thread::message_loop_proxy() or
+// MessageLoopProxy::CreateForCurrentThread().
 class MessageLoopProxy
     : public base::RefCountedThreadSafe<MessageLoopProxy,
                                         MessageLoopProxyTraits> {