Add multiplexing of message pipes in the new EDK.

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 351cbe6d5539ec5e8a4b5d366fac7051820e4ba0..7d8946d7cb4ea6ee67165130c0ff4337433103dd 100644
--- a/mojo/edk/system/broker_messages.h
+++ b/mojo/edk/system/broker_messages.h
@@ -8,6 +8,7 @@
 #include <stdint.h>
 
 #include "base/compiler_specific.h"
+#include "base/process/process_handle.h"
 
 namespace mojo {
 namespace edk {
@@ -15,7 +16,11 @@ namespace edk {
 // This header defines the message format between ChildBroker and
 // ChildBrokerHost.
 
-enum MessageId {
+#if defined(OS_WIN)
+// Windows only messages needed because sandboxed child processes need the
+// parent's help. They are sent synchronously from child to parent and each have
+// a response. They are sent over a raw pipe.
+enum WindowsSandboxMessages {
   // The reply is two HANDLEs.
   CREATE_PLATFORM_CHANNEL_PAIR = 0,
   // The reply is tokens of the same count of passed in handles.
@@ -28,17 +33,48 @@ enum MessageId {
 
 struct BrokerMessage {
   uint32_t size;
-  MessageId id;
+  WindowsSandboxMessages id;
   // Data, if any, follows.
   union {
-#if defined(OS_WIN)
     HANDLE handles[1];  // If HANDLE_TO_TOKEN.
     uint64_t tokens[1];  // If TOKEN_TO_HANDLE.
-#endif
   };
 };
 
-const int kBrokerMessageHeaderSize = sizeof(uint32_t) + sizeof(MessageId);
+const int kBrokerMessageHeaderSize =
+  sizeof(uint32_t) + sizeof(WindowsSandboxMessages);
+
+#endif
+
+// Multiplexing related messages. They are all asynchronous messages.
+// They are sent over RawChannel.
+enum MultiplexMessages {
+  // Messages from child to parent.
+  CONNECT_MESSAGE_PIPE = 0,
+  CANCEL_CONNECT_MESSAGE_PIPE,
+
+  // Messages from parent to child.
+  CONNECT_TO_PROCESS,
+  PEER_PIPE_CONNECTED,
+};
+
+struct ConnectMessagePipeMessage {
+  // CONNECT_MESSAGE_PIPE or CANCEL_CONNECT_MESSAGE_PIPE
+  MultiplexMessages type;
+  uint64_t pipe_id;
+};
+
+struct ConnectToProcessMessage {
+  MultiplexMessages type;  // CONNECT_TO_PROCESS
+  base::ProcessId process_id;
+  // Also has an attached platform handle.
+};
+
+struct PeerPipeConnectedMessage {
+  MultiplexMessages type;  // PEER_PIPE_CONNECTED
+  uint64_t pipe_id;
+  base::ProcessId process_id;
+};
 
 }  // namespace edk
 }  // namespace mojo