Return NULL from base::Thread::message_loop_proxy() when thread is not started.

base/threading/thread.h

Index: base/threading/thread.h
diff --git a/base/threading/thread.h b/base/threading/thread.h
index be8cc8f97a503a7a659ae862dfe9e53bc904a280..aa7d21181766e2dc2952278d0ecc313051ec80dd 100644
--- a/base/threading/thread.h
+++ b/base/threading/thread.h
@@ -117,9 +117,8 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
   // non-NULL after a successful call to Start. After Stop has been called,
   // this will return NULL. Callers can hold on to this even after the thread
   // is gone.
-  // TODO(sanjeevr): Look into merging MessageLoop and MessageLoopProxy.
   scoped_refptr<MessageLoopProxy> message_loop_proxy() const {
-    return message_loop_->message_loop_proxy();
+    return message_loop_ ? message_loop_->message_loop_proxy() : NULL;
   }
 
   // Returns the name of this thread (for display in debugger too).