content: Improve thread priority for raster threads.

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 0746e713f20785915aada189dc328dcd5bdd1aa2..43fe6402a7ec940ad1b64564a54afaae2693bcba 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -828,15 +828,7 @@ void RenderThreadImpl::Init() {
   are_image_decode_tasks_enabled_ = true;
 #endif
 
-  base::SimpleThread::Options thread_options;
-#if defined(OS_ANDROID) || defined(OS_LINUX)
-  if (!command_line.HasSwitch(
-          switches::kUseNormalPriorityForTileTaskWorkerThreads)) {
-    thread_options.set_priority(base::ThreadPriority::BACKGROUND);
-  }
-#endif
-
-  raster_worker_pool_->Start(num_raster_threads, thread_options);
+  raster_worker_pool_->Start(num_raster_threads);
 
   // TODO(boliu): In single process, browser main loop should set up the
   // discardable memory manager, and should skip this if kSingleProcess.