Worker: Introduce per-global-scope task scheduler

third_party/WebKit/Source/core/workers/WorkerBackingThread.h

Index: third_party/WebKit/Source/core/workers/WorkerBackingThread.h
diff --git a/third_party/WebKit/Source/core/workers/WorkerBackingThread.h b/third_party/WebKit/Source/core/workers/WorkerBackingThread.h
index 7280c3f497fb396485dbaec11028b610f99628c5..1418c718a35ffe0a4321470a7b4c1197cff201cf 100644
--- a/third_party/WebKit/Source/core/workers/WorkerBackingThread.h
+++ b/third_party/WebKit/Source/core/workers/WorkerBackingThread.h
@@ -16,6 +16,10 @@
 
 namespace blink {
 
+namespace scheduler {
+class WorkerGlobalScopeScheduler;
+}  // namespace scheduler
+
 class WebThread;
 class WebThreadSupportingGC;
 
@@ -54,6 +58,9 @@ class CORE_EXPORT WorkerBackingThread final {
   void Initialize();
   void Shutdown();
 
+  std::unique_ptr<scheduler::WorkerGlobalScopeScheduler>
+  CreateGlobalScopeScheduler();
+
   WebThreadSupportingGC& BackingThread() {
     DCHECK(backing_thread_);
     return *backing_thread_;