Mojo: Move system embedder API files to mojo/system/embedder.

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(
-    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_