[scheduler] Remove webthread_impl_for_worker_scheduler from public API.

third_party/WebKit/public/platform/scheduler/child/webthread_base.h

Index: third_party/WebKit/public/platform/scheduler/child/webthread_base.h
diff --git a/third_party/WebKit/public/platform/scheduler/child/webthread_base.h b/third_party/WebKit/public/platform/scheduler/child/webthread_base.h
index a1d40bff298425a75acf65652f3ce3218aee0f7f..3b7a42012180c5819552977344d45f734efed68e 100644
--- a/third_party/WebKit/public/platform/scheduler/child/webthread_base.h
+++ b/third_party/WebKit/public/platform/scheduler/child/webthread_base.h
@@ -18,10 +18,17 @@ namespace scheduler {
 class SingleThreadIdleTaskRunner;
 class TaskTimeObserver;
 
+// TODO(scheduler-dev): Do not expose this class in Blink public API.
 class BLINK_PLATFORM_EXPORT WebThreadBase : public WebThread {
  public:
   ~WebThreadBase() override;
 
+  static std::unique_ptr<WebThreadBase> CreateWorkerThread(
+      const char* name,
+      base::Thread::Options options);
+  static std::unique_ptr<WebThreadBase> CreateCompositorThread(
+      base::Thread::Options options);
+
   // WebThread implementation.
   bool IsCurrentThread() const override;
   PlatformThreadId ThreadId() const override = 0;
@@ -43,6 +50,8 @@ class BLINK_PLATFORM_EXPORT WebThreadBase : public WebThread {
   // this thread. Can be called from any thread.
   virtual scheduler::SingleThreadIdleTaskRunner* GetIdleTaskRunner() const = 0;
 
+  virtual void Init() = 0;
+
  protected:
   class TaskObserverAdapter;