Add PTHREAD_PRIO_INHERIT Locks for Mac

base/synchronization/lock.h

Index: base/synchronization/lock.h
diff --git a/base/synchronization/lock.h b/base/synchronization/lock.h
index fbf6cef76911c80332da1524beeb23fd14737917..fb15c66004457f91ef19080e6d7ff7a38c1c09f1 100644
--- a/base/synchronization/lock.h
+++ b/base/synchronization/lock.h
@@ -14,6 +14,22 @@
 
 namespace base {
 
+#if defined(OS_POSIX)
+
+// Determines which platforms can consider using priority inheritance locks. If
+// priority inheritance is possible, it does not necessarily mean it's
+// available. Lock::PriorityInheritanceAvailable must still be checked.
+// If you do not require the conditional inclusion at compile time,
+// simply call Lock::PriorityInheritanceAvailable, which will provide the same
+// result.
+#if defined(OS_NACL) || defined(OS_ANDROID)
+#define PRIORITY_INHERITANCE_LOCKS_POSSIBLE() 0
+#else
+#define PRIORITY_INHERITANCE_LOCKS_POSSIBLE() 1
+#endif
+
+#endif
+
 // A convenient wrapper for an OS specific critical section.  The only real
 // intelligence in this class is in debug mode for the support for the
 // AssertAcquired() method.
@@ -61,6 +77,14 @@ class BASE_EXPORT Lock {
   void AssertAcquired() const;
 #endif  // DCHECK_IS_ON()
 
+#if defined(OS_POSIX)
+  // Whether this platform has priority inheritance available. All locks will
+  // attempt to use the priority inheritance version if available.
+  static bool PriorityInheritanceAvailable() {
+    return internal::LockImpl::PriorityInheritanceAvailable();
+  }
+#endif
+
 #if defined(OS_POSIX) || defined(OS_WIN)
   // Both Windows and POSIX implementations of ConditionVariable need to be
   // able to see our lock and tweak our debugging counters, as they release and