content: Implement dynamic priorities for raster threads.

base/threading/platform_thread_mac.mm

Index: base/threading/platform_thread_mac.mm
diff --git a/base/threading/platform_thread_mac.mm b/base/threading/platform_thread_mac.mm
index 7ab47cb4c6c64ae4a6a4b4076c5d034fd9ce200a..6811eb3e4f72e0bbc72c074d7b97e63439e51c33 100644
--- a/base/threading/platform_thread_mac.mm
+++ b/base/threading/platform_thread_mac.mm
@@ -181,6 +181,15 @@ ThreadPriority PlatformThread::GetCurrentThreadPriority() {
   return ThreadPriority::NORMAL;
 }
 
+// static
+bool PlatformThread::SetChildThreadPriorityInCurrentProcess(
+    PlatformThreadHandle thread_handle,
+    PlatformThreadId tid,
+    ThreadPriority priority) {
+  NOTIMPLEMENTED();
+  return false;
+}
+
 size_t GetDefaultThreadStackSize(const pthread_attr_t& attributes) {
 #if defined(OS_IOS)
   return 0;