Deduplicate PlatformThread's POSIX implementations of SetThreadPriority.

base/threading/platform_thread_internal_posix.h

+// Copyright 2015 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_THREADING_PLATFORM_THREAD_INTERNAL_POSIX_H_
+#define BASE_THREADING_PLATFORM_THREAD_INTERNAL_POSIX_H_
+
+#include "base/threading/platform_thread.h"
+
+namespace base {
+
+namespace internal {
+
+struct ThreadPriorityToNiceValuePair {
+  ThreadPriority priority;
+  int nice_value;
+};
+extern const ThreadPriorityToNiceValuePair kThreadPriorityToNiceValueMap[4];
+
+// Returns the nice value matching |priority| based on the platform-specific
+// implementation of kThreadPriorityToNiceValueMap.
+int ThreadPriorityToNiceValue(ThreadPriority priority);
+
+// Allows platform specific tweaks to the generic POSIX solution for
+// SetThreadPriority. Returns true if the platform-specific implementation
+// handled this |priority| change, false if the generic implementation should
+// instead proceed.
+bool HandleSetThreadPriorityForPlatform(PlatformThreadHandle handle,
+                                        ThreadPriority priority);
+
+}  // namespace internal
+
+}  // namespace base
+
+#endif  // BASE_THREADING_PLATFORM_THREAD_INTERNAL_POSIX_H_