Thread state fixes.

Attaching a native thread should give you a thread in the kNative state.
To be able to run managed code when a thread detaches, we need to be in
the kRunnable state.

Change-Id: I9c8048469d0e2d2a53e8fd85261975bbffe16b4f
diff --git a/src/thread_list.h b/src/thread_list.h
index 7840f71..e83b043 100644
--- a/src/thread_list.h
+++ b/src/thread_list.h
@@ -39,7 +39,7 @@
   void SuspendAll();
   void RunWhileSuspended(Thread* thread, void (*callback)(void*), void* arg);
 
-  void Register(Thread* thread);
+  void Register();
   void Unregister();
 
   void VisitRoots(Heap::RootVisitor* visitor, void* arg) const;