Add support for threadsafe completion callback factory.

ppapi/utility/threading/lock.h

Index: ppapi/utility/threading/lock.h
diff --git a/ppapi/utility/threading/lock.h b/ppapi/utility/threading/lock.h
new file mode 100644
index 0000000000000000000000000000000000000000..71a9876ec9363809a019d989f3322c4efa056bfc
--- /dev/null
+++ b/ppapi/utility/threading/lock.h
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+// 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.
+
+#ifndef PPAPI_UTILITY_THREADING_LOCK_H_
+#define PPAPI_UTILITY_THREADING_LOCK_H_
+
+#ifdef WIN32
+#include <windows.h>
+#else
+#include <pthread.h>
+#endif
+
+namespace pp {
+
+/// A simple wrapper around a platform-specific lock. See also AutoLock.
+class Lock {
+ public:
+  /// Creates a lock in the "not held" state.
+  Lock();
+
+  /// Destroys the lock.
+  ~Lock();
+
+  /// Acquires the lock, blocking if it's already held by a different thread.
+  /// The lock must not already be held on the current thread (i.e. recursive
+  /// locks are not supported).
+  ///
+  /// Most callers should consider using an AutoLock instead to automatically
+  /// acquire and release the lock.
+  void Acquire();
+
+  /// Releases the lock. This must be paired with a call to Acquire().
+  void Release();
+
+ private:
+#if defined(WIN32)
+  typedef CRITICAL_SECTION OSLockType;
+#else
+  typedef pthread_mutex_t OSLockType;
+#endif
+
+  OSLockType os_lock_;
+
+  // Copy and assign not supported.
+  Lock(const Lock&);
+  Lock& operator=(const Lock&);
+};
+
+/// A helper class that scopes holding a lock.
+///
+/// @code
+///   class MyClass {
+///    public:
+///     void DoSomething() {
+///       pp::AutoLock lock(lock_);
+///       ...do something with the lock held...
+///     }
+///
+///    private:
+///     pp::Lock lock_;
+///   };
+/// @endcode
+class AutoLock {
+ public:
+  explicit AutoLock(Lock& lock) : lock_(lock) {
+    lock_.Acquire();
+  }
+
+  ~AutoLock() {
+    lock_.Release();
+  }
+
+ private:
+  Lock& lock_;
+
+  // Copy and assign not supported.
+  AutoLock(const AutoLock&);
+  AutoLock& operator=(const AutoLock&);
+};
+
+}  // namespace pp
+
+#endif  // PPAPI_UTILITY_THREADING_LOCK_H_