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

mojo/edk/test/multiprocess_test_helper.cc

Index: mojo/edk/test/multiprocess_test_helper.cc
diff --git a/mojo/edk/test/multiprocess_test_helper.cc b/mojo/edk/test/multiprocess_test_helper.cc
index 4819a46e12b973629b8065a2972f124f60ca7c43..35fc25417a67d836c28f45fca0688b40a8e42e0b 100644
--- a/mojo/edk/test/multiprocess_test_helper.cc
+++ b/mojo/edk/test/multiprocess_test_helper.cc
@@ -8,18 +8,19 @@
 #include "base/logging.h"
 #include "base/posix/global_descriptors.h"
 #include "base/test/test_timeouts.h"
-#include "mojo/edk/embedder/platform_channel_pair.h"
 #include "mojo/edk/platform/platform_handle.h"
+#include "mojo/edk/platform/platform_pipe.h"
 #include "mojo/edk/platform/scoped_platform_handle.h"
 
 using mojo::platform::PlatformHandle;
+using mojo::platform::PlatformPipe;
 using mojo::platform::ScopedPlatformHandle;
 
 namespace mojo {
 namespace test {
 
 MultiprocessTestHelper::MultiprocessTestHelper()
-    : platform_channel_pair_(new embedder::PlatformChannelPair()) {
+    : platform_channel_pair_(new PlatformPipe()) {
   server_platform_handle = platform_channel_pair_->handle0.Pass();
 }