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

mojo/edk/system/message_pipe.cc

Index: mojo/edk/system/message_pipe.cc
diff --git a/mojo/edk/system/message_pipe.cc b/mojo/edk/system/message_pipe.cc
index 12239b0aff790123e0f60560bac8fd460830588d..26f93cbd076d3069e020c98766e4e807c5b54748 100644
--- a/mojo/edk/system/message_pipe.cc
+++ b/mojo/edk/system/message_pipe.cc
@@ -19,7 +19,7 @@
 #include "mojo/edk/system/proxy_message_pipe_endpoint.h"
 #include "mojo/edk/util/make_unique.h"
 
-using mojo::embedder::ScopedPlatformHandle;
+using mojo::platform::ScopedPlatformHandle;
 using mojo::util::MakeRefCounted;
 using mojo::util::MakeUnique;
 using mojo::util::MutexLocker;