Fix Mojo broker crash on Windows.

mojo/edk/system/broker_messages.h

Index: mojo/edk/system/broker_messages.h
diff --git a/mojo/edk/system/broker_messages.h b/mojo/edk/system/broker_messages.h
index 0ce0960d685b9fadc8e0cb5c1c0c7adf936bfd2c..13fe98014c0df407bbf7abaa056fffec0e720601 100644
--- a/mojo/edk/system/broker_messages.h
+++ b/mojo/edk/system/broker_messages.h
@@ -53,12 +53,31 @@ const uint64_t kBrokerRouteId = 1;
 // They are sent over RawChannel.
 enum MultiplexMessages {
   // Messages from child to parent.
+
+  // Tells the parent that the given pipe id has been bound to a
+  // MessagePipeDispatcher in the child process. The parent will then respond
+  // with either PEER_PIPE_CONNECTED or PEER_DIED when the other side is also
+  // bound.
   CONNECT_MESSAGE_PIPE = 0,
+  // Tells the parent to remove its bookkeeping for the given peer id since
+  // another MessagePipeDispatcher has connected to the pipe in the same
+  // process.
   CANCEL_CONNECT_MESSAGE_PIPE,
 
+
   // Messages from parent to child.
+
+  // Tells the child to open a channel to a given process. This will be followed
+  // by a PEER_PIPE_CONNECTED connecting a message pipe from the child process
+  // to the given process over the new channel.
   CONNECT_TO_PROCESS,
+
+  // Connect a given message pipe to another process.
   PEER_PIPE_CONNECTED,
+
+  // Informs the child that the other end of the message pipe is in a process
+  // that died.
+  PEER_DIED,
 };
 
 struct ConnectMessagePipeMessage {
@@ -79,6 +98,11 @@ struct PeerPipeConnectedMessage {
   base::ProcessId process_id;
 };
 
+struct PeerDiedMessage {
+  MultiplexMessages type;  // PEER_DIED
+  uint64_t pipe_id;
+};
+
 }  // namespace edk
 }  // namespace mojo