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

mojo/edk/system/master_connection_manager.cc

Index: mojo/edk/system/master_connection_manager.cc
diff --git a/mojo/edk/system/master_connection_manager.cc b/mojo/edk/system/master_connection_manager.cc
index caf19b5f568f931062ac526f0a8e6ca8b4cdd95a..ee175b76917a04b29a9581a734be2936e244cb0c 100644
--- a/mojo/edk/system/master_connection_manager.cc
+++ b/mojo/edk/system/master_connection_manager.cc
@@ -11,9 +11,9 @@
 
 #include "base/logging.h"
 #include "mojo/edk/embedder/master_process_delegate.h"
-#include "mojo/edk/embedder/platform_channel_pair.h"
 #include "mojo/edk/platform/io_thread.h"
 #include "mojo/edk/platform/platform_handle.h"
+#include "mojo/edk/platform/platform_pipe.h"
 #include "mojo/edk/platform/thread.h"
 #include "mojo/edk/system/connection_manager_messages.h"
 #include "mojo/edk/system/message_in_transit.h"
@@ -25,6 +25,7 @@
 
 using mojo::platform::PlatformHandle;
 using mojo::platform::PlatformHandleWatcher;
+using mojo::platform::PlatformPipe;
 using mojo::platform::ScopedPlatformHandle;
 using mojo::platform::TaskRunner;
 using mojo::platform::Thread;
@@ -631,7 +632,7 @@ ConnectionManager::Result MasterConnectionManager::ConnectImplHelperNoLock(
           peer_process_identifier,
           ProcessConnections::ConnectionStatus::RUNNING,
           ScopedPlatformHandle());
-      embedder::PlatformChannelPair platform_channel_pair;
+      PlatformPipe platform_channel_pair;
       *platform_handle = platform_channel_pair.handle0.Pass();
 
       connections_[peer_process_identifier]->AddConnection(