base: Fix DCHECK when thread creation fails

base/message_loop/message_loop.cc

Index: base/message_loop/message_loop.cc
diff --git a/base/message_loop/message_loop.cc b/base/message_loop/message_loop.cc
index cfa86d98ce4351137eb9d222af17ed5e7fc30780..d79b26eed2926dad0c70cc562a4a69efbeddca69 100644
--- a/base/message_loop/message_loop.cc
+++ b/base/message_loop/message_loop.cc
@@ -135,7 +135,7 @@ MessageLoop::MessageLoop(scoped_ptr<MessagePump> pump)
 MessageLoop::~MessageLoop() {
   // current() could be NULL if this message loop is destructed before it is
   // bound to a thread.
-  DCHECK(current() == this || !current());
+  DCHECK(current() == this || !pump_);

[danakj, 2016/01/05 19:40:15]

This no longer captures that current() is either |this| or |nullptr| though, but
the comment claims current() would be NULL otherwise.

I believe that this comment is wrong and current() may be some other message
loop if pump_ is not set which means BindToCurrentThread() was never called for
this MessageLoop yet. Can you confirm and fix the comment?

[Sami, 2016/01/06 10:56:19]

You're right, I just noticed the same thing while adding a test. I think the
main scenarios are:

1) The loop has been bound and is the current one.
2) The loop hasn't been bound and there is another current loop.
3) The loop hasn't been bound and there's no other loop either.

I've changed the comment and the logic accordingly.

 
   // iOS just attaches to the loop, it doesn't Run it.
   // TODO(stuartmorgan): Consider wiring up a Detach().