[scheduler] Remove WebThreadImplForUtilityThread from public API.

third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc

Index: third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc
diff --git a/third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc b/third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc
index d8f19ee3c3c04adfa00d760a1e6212068f278e68..dbbc513132b399c2aef139ce27ed86d946da8e53 100644
--- a/third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc
+++ b/third_party/WebKit/Source/platform/scheduler/child/webthread_base.cc
@@ -13,6 +13,7 @@
 #include "base/pending_task.h"
 #include "base/threading/platform_thread.h"
 #include "platform/scheduler/child/webthread_impl_for_worker_scheduler.h"
+#include "platform/scheduler/utility/webthread_impl_for_utility_thread.h"
 #include "public/platform/WebTraceLocation.h"
 #include "public/platform/scheduler/child/compositor_worker_scheduler.h"
 #include "public/platform/scheduler/child/single_thread_idle_task_runner.h"
@@ -135,5 +136,9 @@ std::unique_ptr<WebThreadBase> WebThreadBase::CreateCompositorThread(
   return base::MakeUnique<WebThreadForCompositor>(options);
 }
 
+std::unique_ptr<WebThreadBase> WebThreadBase::InitializeUtilityThread() {
+  return base::MakeUnique<WebThreadImplForUtilityThread>();
+}
+
 }  // namespace scheduler
 }  // namespace blink