Implement the infrastructure of creating WorkerFetchContext in worker global scope.

third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h

Index: third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h
diff --git a/third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h b/third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h
index 63062cf4cea0399fc338d503ac418b8c4797c14b..90bc12be729205d5f103daca30d7ef883563577f 100644
--- a/third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h
+++ b/third_party/WebKit/public/web/modules/serviceworker/WebServiceWorkerContextClient.h
@@ -35,6 +35,7 @@
 
 #include "public/platform/WebMessagePortChannel.h"
 #include "public/platform/WebURL.h"
+#include "public/platform/WebWorkerFetchContext.h"
 #include "public/platform/modules/serviceworker/WebServiceWorkerClientsClaimCallbacks.h"
 #include "public/platform/modules/serviceworker/WebServiceWorkerClientsInfo.h"
 #include "public/platform/modules/serviceworker/WebServiceWorkerEventResult.h"
@@ -244,6 +245,14 @@ class WebServiceWorkerContextClient {
     return nullptr;
   }
 
+  // Creates a WebWorkerFetchContext for a service worker. Ownership of the
+  // returned object is transferred to the caller. This is called on the main
+  // thread. This is used only when off-main-thread-fetch is enabled.
+  virtual std::unique_ptr<blink::WebWorkerFetchContext>
+  CreateServiceWorkerFetchContext() {
+    return nullptr;
+  }
+
   // Ownership of the returned object is transferred to the caller.
   // This is called on the main thread.
   virtual WebServiceWorkerProvider* CreateServiceWorkerProvider() {