[cros] Add RecursiveLock for CrOS implementation.

rlz/lib/recursive_lock.cc

Index: rlz/lib/recursive_lock.cc
diff --git a/rlz/lib/recursive_lock.cc b/rlz/lib/recursive_lock.cc
new file mode 100644
index 0000000000000000000000000000000000000000..686cf0ebba26da2688f4fe204742c75009b57971
--- /dev/null
+++ b/rlz/lib/recursive_lock.cc
@@ -0,0 +1,40 @@
+// Copyright (c) 2012 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 "rlz/lib/recursive_lock.h"
+
+#include "base/logging.h"
+
+namespace rlz_lib {
+
+RecursiveLock::RecursiveLock()
+    : owner_(),
+      recursion_() {
+}
+
+RecursiveLock::~RecursiveLock() {
+}
+
+void RecursiveLock::Acquire() {
+  base::subtle::Atomic32 me = base::PlatformThread::CurrentId();
+  if (me != base::subtle::NoBarrier_Load(&owner_)) {
+    lock_.Acquire();
+    DCHECK(!recursion_);
+    DCHECK(!owner_);
+    base::subtle::NoBarrier_Store(&owner_, me);
+  }
+  ++recursion_;
+}
+
+void RecursiveLock::Release() {
+  DCHECK_EQ(base::subtle::NoBarrier_Load(&owner_),
+            base::PlatformThread::CurrentId());
+  DCHECK_GT(recursion_, 0);
+  if (!--recursion_) {
+    base::subtle::NoBarrier_Store(&owner_, 0);
+    lock_.Release();
+  }
+}
+
+}  // namespace rlz_lib