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

mojo/edk/embedder/BUILD.gn

 # 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.
 
 import("../mojo_edk.gni")
 
 # TODO(vtl): Move multiprocess stuff into a separate target.
 mojo_edk_source_set("embedder") {
   # This isn't really a standalone target; it must be linked into the
   # mojo_system_impl component.
@@ skipping 37 matching lines @@
 }
 
 mojo_edk_source_set("platform") {
   # This isn't really a standalone target; it must be linked into the
   # mojo_system_impl component.
   visibility = [ ":embedder" ]
 
   mojo_edk_visibility = [ "mojo/edk/system/*" ]
 
   sources = [
-    "platform_channel_pair.cc",
-    "platform_channel_pair.h",
     "platform_channel_utils.cc",
     "platform_channel_utils.h",
     "platform_support.h",
     "simple_platform_shared_buffer.cc",
     "simple_platform_shared_buffer.h",
     "simple_platform_support.cc",
     "simple_platform_support.h",
   ]
 
   mojo_sdk_public_deps = [ "mojo/public/cpp/system" ]
@@ skipping 44 matching lines @@
   ]
 
   mojo_edk_deps = [
     "mojo/edk/base_edk",
     "mojo/edk/test:test_support",
     "mojo/edk/system",
     "mojo/edk/system/test",
     "mojo/edk/util",
   ]
 }