Move PlatformChannelPair to //mojo/edk/platform and rename it PlatformPipe.

mojo/edk/embedder/platform_channel_pair.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_EDK_EMBEDDER_PLATFORM_CHANNEL_PAIR_H_
-#define MOJO_EDK_EMBEDDER_PLATFORM_CHANNEL_PAIR_H_
-
-#include "mojo/edk/platform/scoped_platform_handle.h"
-
-namespace mojo {
-namespace embedder {
-
-// A helper class for creating a pair of |PlatformHandle|s that are connected by
-// a suitable (platform-specific) bidirectional "pipe" (e.g., Unix domain
-// socket). The resulting handles can then be used in the same process (e.g., in
-// tests) or between processes.
-//
-// Note: On POSIX platforms, to write to the "pipe", use
-// |PlatformChannel{Write,Writev}()| (from platform_channel_utils.h) instead of
-// |write()|, |writev()|, etc. Otherwise, you have to worry about platform
-// differences in suppressing |SIGPIPE|.
-class PlatformChannelPair {
- public:
-  PlatformChannelPair();
-  ~PlatformChannelPair();
-
-  platform::ScopedPlatformHandle handle0;
-  platform::ScopedPlatformHandle handle1;
-};
-
-}  // namespace embedder
-}  // namespace mojo
-
-#endif  // MOJO_EDK_EMBEDDER_PLATFORM_CHANNEL_PAIR_H_