Partially implement WorkerFetchContext and WorkerThreadableLoadingContext and add virtual tests

third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h

Index: third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h
diff --git a/third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h b/third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h
index 34478355aef06e70d50fe46e846fc8a14f80a243..35549a90062bec4abbbf1ef484dda40ba66bca84 100644
--- a/third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h
+++ b/third_party/WebKit/Source/core/loader/ThreadableLoadingContext.h
@@ -19,6 +19,7 @@ class Document;
 class ResourceFetcher;
 class SecurityOrigin;
 class WebTaskRunner;
+class WorkerGlobalScope;
 
 // An abstract interface for top-level loading context.
 // This should be accessed only from the thread where the loading
@@ -29,6 +30,7 @@ class CORE_EXPORT ThreadableLoadingContext
 
  public:
   static ThreadableLoadingContext* Create(Document&);
+  static ThreadableLoadingContext* Create(WorkerGlobalScope&);
 
   ThreadableLoadingContext() = default;
   virtual ~ThreadableLoadingContext() = default;