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diff --git a/chromium/mojo/public/cpp/utility/mutex.h b/chromium/mojo/public/cpp/utility/mutex.h
new file mode 100644
index 00000000000..35611c2ba9a
--- /dev/null
+++ b/chromium/mojo/public/cpp/utility/mutex.h
@@ -0,0 +1,70 @@
+// Copyright 2014 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 MOJO_PUBLIC_CPP_UTILITY_MUTEX_H_
+#define MOJO_PUBLIC_CPP_UTILITY_MUTEX_H_
+
+#ifdef _WIN32
+#error "Not implemented: See crbug.com/342893."
+#endif
+
+#include <pthread.h>
+
+#include "mojo/public/cpp/system/macros.h"
+
+namespace mojo {
+
+#ifdef NDEBUG
+// Note: Make a C++ constant for |PTHREAD_MUTEX_INITIALIZER|. (We can't directly
+// use the C macro in an initializer list, since it might expand to |{ ... }|.)
+namespace internal {
+const pthread_mutex_t kPthreadMutexInitializer = PTHREAD_MUTEX_INITIALIZER;
+}
+#endif
+
+class Mutex {
+ public:
+#ifdef NDEBUG
+  Mutex() : mutex_(internal::kPthreadMutexInitializer) {}
+  ~Mutex() { pthread_mutex_destroy(&mutex_); }
+
+  void Lock() { pthread_mutex_lock(&mutex_); }
+  void Unlock() { pthread_mutex_unlock(&mutex_); }
+  bool TryLock() { return pthread_mutex_trylock(&mutex_) == 0; }
+
+  void AssertHeld() {}
+#else
+  Mutex();
+  ~Mutex();
+
+  void Lock();
+  void Unlock();
+  bool TryLock();
+
+  void AssertHeld();
+#endif
+
+ private:
+  pthread_mutex_t mutex_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(Mutex);
+};
+
+class MutexLock {
+ public:
+  explicit MutexLock(Mutex* mutex) : mutex_(mutex) { mutex_->Lock(); }
+  ~MutexLock() { mutex_->Unlock(); }
+
+ private:
+  Mutex* const mutex_;
+
+  MOJO_DISALLOW_COPY_AND_ASSIGN(MutexLock);
+};
+
+// Catch bug where variable name is omitted (e.g., |MutexLock (&mu)|).
+#define MutexLock(x) MOJO_COMPILE_ASSERT(0, mutex_lock_missing_variable_name);
+
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_UTILITY_MUTEX_H_