Mojo: Add the ability to hook up a channel to the embedder API.

mojo/system/embedder.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MOJO_SYSTEM_EMBEDDER_H_
 #define MOJO_SYSTEM_EMBEDDER_H_
 
+#include "base/callback.h"
+#include "base/memory/ref_counted.h"
+#include "base/task_runner.h"
+#include "mojo/public/system/core.h"
+#include "mojo/system/scoped_platform_handle.h"
 #include "mojo/system/system_impl_export.h"
 
 namespace mojo {
 namespace embedder {
 
+// Must be called first to initialize the (global, singleton) system.
 MOJO_SYSTEM_IMPL_EXPORT void Init();
 
+// Creates a new "channel", returning a handle to the bootstrap message pipe on
+// that channel. |platform_handle| should be an OS-dependent handle to one side
+// of a suitable bidirectional OS "pipe" (e.g., a file descriptor to a socket on
+// POSIX, a handle to a named pipe on Windows); this "pipe" should be connected
+// and ready for operation (e.g., to be written to or read from).
+// |io_thread_task_runner| should be a |TaskRunner| for the thread on which the
+// "channel" will run (read data and demultiplex).
+//
+// Returns |MOJO_HANDLE_INVALID| on error. Note that this will happen only if,
+// e.g., the handle table is full (operation of the channel begins
+// asynchronously and if, e.g., the other end of the "pipe" is closed, this will
+// report an error to the returned handle in the usual way).
+//
+// Notes: The handle returned is ready for use immediately, with messages
+// written to it queued. E.g., it would be perfectly valid for a message to be
+// immediately written to the returned handle and the handle closed, all before
+// the channel has begun operation on the IO thread. In this case, the channel
+// is expected to connect as usual, send the queued message, and report that the
+// handle was closed to the other side. (This message may well contain another
+// handle, so there may well still be message pipes "on" this channel.)
+//
+// TODO(vtl): Figure out channel teardown.
+struct ChannelInfo;
+typedef base::Callback<void(ChannelInfo*)> DidCreateChannelOnIOThreadCallback;
+MOJO_SYSTEM_IMPL_EXPORT MojoHandle CreateChannel(
+    system::ScopedPlatformHandle platform_handle,
+    scoped_refptr<base::TaskRunner> io_thread_task_runner,
+    DidCreateChannelOnIOThreadCallback callback);
+
+MOJO_SYSTEM_IMPL_EXPORT void DestroyChannelOnIOThread(
+    ChannelInfo* channel_info);
+
 }  // namespace embedder
 }  // namespace mojo
 
 #endif  // MOJO_SYSTEM_EMBEDDER_H_