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..62a65400df5df5ca363f1a2b635176d8f5b835ca 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. Use

[danakj, 2016/07/29 21:06:40]

OK my only nit is that I rather this lives in lock_impl_posix.cc and is an
implementation detail until we need it outside. LGTM otherwise.

[robliao, 2016/07/29 21:22:53]

sgtm. Moved and adjusted the comment for the more local scope.

+// this define for platform code that may not compile if priority inheritance
+// locks aren't available. Lock::PriorityInheritanceAvailable still must be
+// checked as the code may compile but the underlying platform still may not
+// support priority inheritance locks. If you do not require the conditional
+// inclusion at compile time, simply call Lock::PriorityInheritanceAvailable.
+#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