compositor-worker: Create a separate CompositorWorkerGlobalScope for compositor workers.

Source/core/workers/DedicatedWorkerGlobalScope.h

Index: Source/core/workers/DedicatedWorkerGlobalScope.h
diff --git a/Source/core/workers/DedicatedWorkerGlobalScope.h b/Source/core/workers/DedicatedWorkerGlobalScope.h
index 08dbe3c8ea17df877c9d4a75cb191e3558b119f4..ff99c61b11c508f981aebb6766fdd67e414b694b 100644
--- a/Source/core/workers/DedicatedWorkerGlobalScope.h
+++ b/Source/core/workers/DedicatedWorkerGlobalScope.h
@@ -41,7 +41,7 @@ namespace blink {
 class DedicatedWorkerThread;
 class WorkerThreadStartupData;
 
-class DedicatedWorkerGlobalScope final : public WorkerGlobalScope {
+class DedicatedWorkerGlobalScope : public WorkerGlobalScope {
     DEFINE_WRAPPERTYPEINFO();
 public:
     typedef WorkerGlobalScope Base;
@@ -66,7 +66,7 @@ public:
 
     DECLARE_VIRTUAL_TRACE();
 
-private:
+protected:
     DedicatedWorkerGlobalScope(const KURL&, const String& userAgent, DedicatedWorkerThread*, double timeOrigin, const SecurityOrigin*, PassOwnPtrWillBeRawPtr<WorkerClients>);
 };