Reland of Initial version of file wrapper

webrtc/base/file.cc

+/*
+ *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "webrtc/base/file.h"
+
+namespace rtc {
+
+File::File(PlatformFile file) : file_(file) {}
+
+File::~File() {
+  Close();
+}
+
+File::File(File&& other) : file_(other.file_) {
+  other.file_ = kInvalidPlatformFileValue;
+}
+
+File& File::operator=(File&& other) {
+  Close();
+  file_ = other.file_;
+  other.file_ = kInvalidPlatformFileValue;
+  return *this;
+}
+
+bool File::IsOpen() {
+  return file_ != kInvalidPlatformFileValue;
+}
+
+}  // namespace rtc