Add multiplexing of message pipes in the new EDK.

mojo/edk/system/dispatcher.h

Index: mojo/edk/system/dispatcher.h
diff --git a/mojo/edk/system/dispatcher.h b/mojo/edk/system/dispatcher.h
index fb757c7c95d0663ccdca118d6ff87495e77563f4..d1c7b1f62548085958d459cff16606c8dd9e9247 100644
--- a/mojo/edk/system/dispatcher.h
+++ b/mojo/edk/system/dispatcher.h
@@ -300,6 +300,7 @@ class MOJO_SYSTEM_IMPL_EXPORT Dispatcher
   // Available to subclasses. (Note: Returns a non-const reference, just like
   // |base::AutoLock|'s constructor takes a non-const reference.)
   base::Lock& lock() const { return lock_; }
+  bool is_closed() const { return is_closed_; }
 
  private:
   friend class DispatcherTransport;