Add support for threadsafe completion callback factory.

ppapi/utility/threading/lock.cc

Index: ppapi/utility/threading/lock.cc
diff --git a/ppapi/utility/threading/lock.cc b/ppapi/utility/threading/lock.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d50782ecdd4ca145063f19e06757c808aefede47
--- /dev/null
+++ b/ppapi/utility/threading/lock.cc
@@ -0,0 +1,49 @@
+// 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 "ppapi/utility/threading/lock.h"
+
+namespace pp {
+
+#ifdef WIN32  // Windows implementation for native plugins.
+
+Lock::Lock() {
+  // The second parameter is the spin count; for short-held locks it avoid the

[viettrungluu, 2012/07/11 00:11:27]

Nit: You missed the s/avoid/avoids/ part.

+  // contending thread from going to sleep which helps performance greatly.
+  ::InitializeCriticalSectionAndSpinCount(&os_lock_, 2000);
+}
+
+Lock::~Lock() {
+  ::DeleteCriticalSection(&os_lock_);
+}
+
+void Lock::Acquire() {
+  ::EnterCriticalSection(&os_lock_);
+}
+
+void Lock::Release() {
+  ::LeaveCriticalSection(&os_lock_);
+}
+
+#else  // Posix implementation.
+
+Lock::Lock() {
+  pthread_mutex_init(&os_lock_, NULL);
+}
+
+Lock::~Lock() {
+  pthread_mutex_destroy(&os_lock_);
+}
+
+void Lock::Acquire() {
+  pthread_mutex_lock(&os_lock_);
+}
+
+void Lock::Release() {
+  pthread_mutex_unlock(&os_lock_);
+}
+
+#endif
+
+}  // namespace pp