Mojo: Move system embedder API files to mojo/system/embedder.

mojo/system/embedder/platform_channel_pair_posix.cc

Index: mojo/system/embedder/platform_channel_pair_posix.cc
diff --git a/mojo/system/platform_channel_pair_posix.cc b/mojo/system/embedder/platform_channel_pair_posix.cc
similarity index 97%
rename from mojo/system/platform_channel_pair_posix.cc
rename to mojo/system/embedder/platform_channel_pair_posix.cc
index 7b7680b119bbc02429204fbd48ebf124468ea044..f6d9b71fd76c708f19eb7b2b9c93a020f204fbd6 100644
--- a/mojo/system/platform_channel_pair_posix.cc
+++ b/mojo/system/embedder/platform_channel_pair_posix.cc
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-#include "mojo/system/platform_channel_pair.h"
+#include "mojo/system/embedder/platform_channel_pair.h"
 
 #include <fcntl.h>
 #include <sys/socket.h>
@@ -13,7 +13,7 @@
 #include "base/logging.h"
 #include "base/posix/global_descriptors.h"
 #include "base/strings/string_number_conversions.h"
-#include "mojo/system/platform_handle.h"
+#include "mojo/system/embedder/platform_handle.h"
 
 namespace mojo {
 namespace embedder {