Add PTHREAD_PRIO_INHERIT to POSIX Locks

base/synchronization/lock.h

Index: base/synchronization/lock.h
diff --git a/base/synchronization/lock.h b/base/synchronization/lock.h
index fbf6cef76911c80332da1524beeb23fd14737917..2ab28c608143c744e603a2d2feb5317fa950877b 100644
--- a/base/synchronization/lock.h
+++ b/base/synchronization/lock.h
@@ -14,6 +14,19 @@
 
 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.

[gab, 2016/06/07 12:28:18]

Why not have everyone go through the method and encode this macro in it?

[robliao, 2016/06/07 14:11:04]

A couple of reasons:
1) Callers who care about this may call libraries that aren't available when
priority inheritance isn't possible at compile time.
2) The sandbox unit tests use this to conditionally include the tests.

I went ahead and included in this check in 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 +74,14 @@ 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