Make MessageLoopProxy::current() usable on threads that don't have MessageLoop.

base/message_loop.cc

Index: base/message_loop.cc
diff --git a/base/message_loop.cc b/base/message_loop.cc
index f60bf69d8302a2c8122cbf26ef5948f340656178..28bcc614cbfa4808131578ce9f6ad70c3f82666f 100644
--- a/base/message_loop.cc
+++ b/base/message_loop.cc
@@ -139,6 +139,7 @@ MessageLoop::MessageLoop(Type type)
   lazy_tls_ptr.Pointer()->Set(this);
 
   message_loop_proxy_ = new base::MessageLoopProxyImpl();
+  base::ThreadMainTaskRunner::SetCurrent(message_loop_proxy_);
 
 // TODO(rvargas): Get rid of the OS guards.
 #if defined(OS_WIN)
@@ -199,6 +200,7 @@ MessageLoop::~MessageLoop() {
                     WillDestroyCurrentMessageLoop());
 
   // Tell the message_loop_proxy that we are dying.
+  base::ThreadMainTaskRunner::SetCurrent(NULL);
   static_cast<base::MessageLoopProxyImpl*>(message_loop_proxy_.get())->
       WillDestroyCurrentMessageLoop();
   message_loop_proxy_ = NULL;