Add Lock::HandlesMultipleThreadPriorities().

base/synchronization/lock.h

 // Copyright (c) 2011 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 BASE_SYNCHRONIZATION_LOCK_H_
 #define BASE_SYNCHRONIZATION_LOCK_H_
 
 #include "base/base_export.h"
 #include "base/logging.h"
 #include "base/macros.h"
@@ skipping 43 matching lines @@
     bool rv = lock_.Try();
     if (rv) {
       CheckUnheldAndMark();
     }
     return rv;
   }
 
   void AssertAcquired() const;
 #endif  // DCHECK_IS_ON()
 
+  // Whether it is safe to use a Lock from different thread priorities (i.e.
+  // there won't be priority inversion for an extended period of time).
+  static bool IsSafeWithMultipleThreadPriorities() {

[robliao, 2016/08/03 18:02:10]

I would go with HandlesMultipleThreadPriorities. Safe is too strong of a
guarantee.

[fdoray, 2016/08/03 18:34:48]

Done.

 #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();
+#else
+    return true;

[gab, 2016/08/03 18:04:57]

Add a comment about why that's true on Windows (summarize and refer to
https://msdn.microsoft.com/library/windows/desktop/ms684831.aspx)

and also 
#elif (OS_WIN) above and 
#else
#error "Unsupported platform"
#endif

[fdoray, 2016/08/03 18:34:48]

Done.

+#endif
   }
-#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
   // acquire locks inside of their condition variable APIs.
   friend class ConditionVariable;
 #endif
 
  private:
 #if DCHECK_IS_ON()
@@ skipping 54 matching lines @@
   }
 
  private:
   Lock& lock_;
   DISALLOW_COPY_AND_ASSIGN(AutoUnlock);
 };
 
 }  // namespace base
 
 #endif  // BASE_SYNCHRONIZATION_LOCK_H_