Add multiplexing of message pipes in the new EDK.

mojo/public/c/system/message_pipe.h

Index: mojo/public/c/system/message_pipe.h
diff --git a/mojo/public/c/system/message_pipe.h b/mojo/public/c/system/message_pipe.h
index d42c3fc65df49c9a41213f2d504f60b1ecbca46e..12309723f8f252b5bd2037e6a9e019d9463eb214 100644
--- a/mojo/public/c/system/message_pipe.h
+++ b/mojo/public/c/system/message_pipe.h
@@ -18,17 +18,26 @@
 //   |uint32_t struct_size|: Set to the size of the
 //       |MojoCreateMessagePipeOptions| struct. (Used to allow for future
 //       extensions.)
-//   |MojoCreateMessagePipeOptionsFlags flags|: Reserved for future use.
+//   |MojoCreateMessagePipeOptionsFlags flags|: Used to specify different modes
+//       of operation.
 //       |MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_NONE|: No flags; default mode.
+//       |MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_TRANSFERABLE|: The message pipe
+//           can be sent over another pipe after it's been read or written. This
+//           mode makes message pipes use more resources (one OS pipe each), so
+//           only specify if this functionality is required.
 
 typedef uint32_t MojoCreateMessagePipeOptionsFlags;
 
 #ifdef __cplusplus
 const MojoCreateMessagePipeOptionsFlags
     MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_NONE = 0;
+const MojoCreateMessagePipeOptionsFlags
+    MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_TRANSFERABLE = 1;
 #else
 #define MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_NONE \
   ((MojoCreateMessagePipeOptionsFlags)0)
+#define MOJO_CREATE_MESSAGE_PIPE_OPTIONS_FLAG_TRANSFERABLE \
+  ((MojoCreateMessagePipeOptionsFlags)1)
 #endif
 
 MOJO_STATIC_ASSERT(MOJO_ALIGNOF(int64_t) == 8, "int64_t has weird alignment");