EDK: Move {platform_handle,scoped_platform_handle}.* to //mojo/edk/platform.

mojo/edk/system/channel.cc

Index: mojo/edk/system/channel.cc
diff --git a/mojo/edk/system/channel.cc b/mojo/edk/system/channel.cc
index 45c58124c97dcce73a1de315a4c866bdea99a1cb..c26a37402246bb98de30127bbab8cd64856f7fa1 100644
--- a/mojo/edk/system/channel.cc
+++ b/mojo/edk/system/channel.cc
@@ -13,7 +13,7 @@
 #include "mojo/edk/system/endpoint_relayer.h"
 #include "mojo/edk/system/transport_data.h"
 
-using mojo::embedder::ScopedPlatformHandle;
+using mojo::platform::ScopedPlatformHandle;
 using mojo::util::MakeRefCounted;
 using mojo::util::MutexLocker;
 using mojo::util::RefPtr;