Partially implement WorkerFetchContext and WorkerThreadableLoadingContext and add virtual tests

third_party/WebKit/Source/core/loader/ThreadableLoader.cpp

Index: third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
diff --git a/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp b/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
index bf836d3d8de9c0974f9523e72bb32f0c5922450c..cb4ce9a72dc23205fd9b71d9a1fff03830a5c478 100644
--- a/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
+++ b/third_party/WebKit/Source/core/loader/ThreadableLoader.cpp
@@ -34,8 +34,10 @@
 #include "core/dom/ExecutionContext.h"
 #include "core/loader/DocumentThreadableLoader.h"
 #include "core/loader/ThreadableLoadingContext.h"
+#include "core/loader/WorkerFetchContext.h"
 #include "core/loader/WorkerThreadableLoader.h"
 #include "core/workers/WorkerGlobalScope.h"
+#include "platform/RuntimeEnabledFeatures.h"
 
 namespace blink {
 
@@ -47,6 +49,14 @@ ThreadableLoader* ThreadableLoader::Create(
   DCHECK(client);
 
   if (context.IsWorkerGlobalScope()) {
+    if (RuntimeEnabledFeatures::offMainThreadFetchEnabled()) {
+      DCHECK(ToWorkerGlobalScope(&context)->GetFetchContext());
+      // TODO(horo): Rename DocumentThreadableLoader. We will use it on the
+      // worker thread when off-main-thread-fetch is enabled.
+      return DocumentThreadableLoader::Create(
+          *ThreadableLoadingContext::Create(*ToWorkerGlobalScope(&context)),
+          client, options, resource_loader_options);
+    }
     return WorkerThreadableLoader::Create(ToWorkerGlobalScope(context), client,
                                           options, resource_loader_options);
   }