Create a reader-writer lock implementaiton in base.

base/synchronization/rw_lock_win.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 "base/synchronization/rw_lock.h"
+
+namespace base {
+
+RWLock::RWLock() : native_handle_(SRWLOCK_INIT) {}
+
+RWLock::~RWLock() = default;
+
+void RWLock::ReadAcquire() {
+  ::AcquireSRWLockShared(&native_handle_);
+}
+
+void RWLock::ReadRelease() {
+  ::ReleaseSRWLockShared(&native_handle_);
+}
+
+void RWLock::WriteAcquire() {
+  ::AcquireSRWLockExclusive(&native_handle_);
+}
+
+void RWLock::WriteRelease() {
+  ::ReleaseSRWLockExclusive(&native_handle_);
+}
+
+}  // namespace base