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

mojo/system/platform_handle.cc

-// Copyright 2013 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 "mojo/system/platform_handle.h"
-
-#include "build/build_config.h"
-#if defined(OS_POSIX)
-#include <unistd.h>
-#elif defined(OS_WIN)
-#include <windows.h>
-#else
-#error "Platform not yet supported."
-#endif
-
-#include "base/compiler_specific.h"
-#include "base/logging.h"
-
-namespace mojo {
-namespace embedder {
-
-void PlatformHandle::CloseIfNecessary() {
-  if (!is_valid())
-    return;
-
-#if defined(OS_POSIX)
-  bool success = (close(fd) == 0);
-  DPCHECK(success);
-  fd = -1;
-#elif defined(OS_WIN)
-  bool success = !!CloseHandle(handle);
-  DPCHECK(success);
-  handle = INVALID_HANDLE_VALUE;
-#else
-#error "Platform not yet supported."
-#endif
-}
-
-}  // namespace embedder
-}  // namespace mojo