Turn ThreadPriority enum into an enum class.

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index d8f7974eabab6941cbb1c269b51f5380a2b016ec..94d089cffe3535d69f2eab21b7fa2de19a1612a7 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -651,7 +651,7 @@ void RenderThreadImpl::Init() {
     if (!command_line.HasSwitch(
             switches::kUseNormalPriorityForTileTaskWorkerThreads)) {
       cc::TileTaskWorkerPool::SetWorkerThreadPriority(
-          base::kThreadPriority_Background);
+          base::ThreadPriority::BACKGROUND);
     }
 #endif
   }
@@ -1005,7 +1005,7 @@ void RenderThreadImpl::EnsureWebKitInitialized() {
       compositor_thread_.reset(new base::Thread("Compositor"));
       compositor_thread_->Start();
 #if defined(OS_ANDROID)
-      compositor_thread_->SetPriority(base::kThreadPriority_Display);
+      compositor_thread_->SetPriority(base::ThreadPriority::DISPLAY);
 #endif
       compositor_message_loop_proxy_ =
           compositor_thread_->message_loop_proxy();