Service Worker: Migrate to version_uuid and surface ServiceWorker.id. (Blink 1/3)

Source/core/fetch/FetchContext.h

Index: Source/core/fetch/FetchContext.h
diff --git a/Source/core/fetch/FetchContext.h b/Source/core/fetch/FetchContext.h
index f912c2150aeab586e3ca81bb67def2a998cd1526..1a3a710a03e4c6db8473ad4d41d7f83a0281263d 100644
--- a/Source/core/fetch/FetchContext.h
+++ b/Source/core/fetch/FetchContext.h
@@ -92,7 +92,7 @@ public:
     virtual bool canRequest(Resource::Type, const ResourceRequest&, const KURL&, const ResourceLoaderOptions&, bool forPreload, FetchRequest::OriginRestriction) const { return false; }
 
     virtual bool isControlledByServiceWorker() const { return false; }
-    virtual int64_t serviceWorkerID() const { return -1; }
+    virtual std::string serviceWorkerID() const { return std::string(); }
 
     virtual bool isMainFrame() const { return true; }
     virtual bool hasSubstituteData() const { return false; }