Make it possible to write a message pipe endpoint's peer into it.

mojo/edk/system/platform_handle_dispatcher.cc

Index: mojo/edk/system/platform_handle_dispatcher.cc
diff --git a/mojo/edk/system/platform_handle_dispatcher.cc b/mojo/edk/system/platform_handle_dispatcher.cc
index f2c6e72cf4cfadd56f6c241fea55b7090aa30dfc..93d2b5cb2c414f189085d54b6f31c048697efa66 100644
--- a/mojo/edk/system/platform_handle_dispatcher.cc
+++ b/mojo/edk/system/platform_handle_dispatcher.cc
@@ -86,8 +86,11 @@ void PlatformHandleDispatcher::CloseImplNoLock() {
 }
 
 RefPtr<Dispatcher>
-PlatformHandleDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock() {
+PlatformHandleDispatcher::CreateEquivalentDispatcherAndCloseImplNoLock(
+    MessagePipe* /*message_pipe*/,
+    unsigned /*port*/) {
   mutex().AssertHeld();
+  CancelAllAwakablesNoLock();
   return Create(platform_handle_.Pass());
 }