[NaCl SDK] Add comments in the implementation code of GoogleDriveFs

native_client_sdk/src/libraries/nacl_io/googledrivefs/googledrivefs.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "nacl_io/googledrivefs/googledrivefs.h"
 
 #include "nacl_io/filesystem.h"
 #include "nacl_io/node.h"
 #include "nacl_io/path.h"
 
 namespace nacl_io {
 
+// This is not further implemented.
+// PNaCl is on a path to deprecation, and WebAssembly is
+// the focused technology.
+
 GoogleDriveFs::GoogleDriveFs() {}
 
 Error GoogleDriveFs::Init(const FsInitArgs& args) {
   // TODO: support init
   LOG_ERROR("init not supported.");
   return EPERM;
 }
 
 Error GoogleDriveFs::OpenWithMode(const Path& path,
                                   int open_flags,
@@ skipping 28 matching lines @@
   return EPERM;
 }
 
 Error GoogleDriveFs::Remove(const Path& path) {
   // TODO: support remove
   LOG_ERROR("remove not supported.");
   return EPERM;
 }
 
 }  // namespace nacl_io