Use tri-state enum for the existence of Fetch Handler in ServiceWorkerVersion.

content/browser/service_worker/service_worker_version.h

Index: content/browser/service_worker/service_worker_version.h
diff --git a/content/browser/service_worker/service_worker_version.h b/content/browser/service_worker/service_worker_version.h
index 0e368ab3c619bd97a8834f44dbbe84ff16382f78..c6dc1eb91de3f5298969696b782c7c78c823a57b 100644
--- a/content/browser/service_worker/service_worker_version.h
+++ b/content/browser/service_worker/service_worker_version.h
@@ -134,8 +134,13 @@ class CONTENT_EXPORT ServiceWorkerVersion
   }
   ServiceWorkerVersionInfo GetInfo();
   Status status() const { return status_; }
-  bool has_fetch_handler() const { return has_fetch_handler_; }
+
+  // This flag is set when the install event has been executed in a new version
+  // or when an installed version is loaded from the storage. When a new version
+  // is not installed yet, returns base::nullopt.
+  base::Optional<bool> has_fetch_handler() const { return has_fetch_handler_; }
   void set_has_fetch_handler(bool has_fetch_handler) {
+    DCHECK(!has_fetch_handler_);
     has_fetch_handler_ = has_fetch_handler;
   }
 
@@ -663,7 +668,7 @@ class CONTENT_EXPORT ServiceWorkerVersion
   const GURL scope_;
   std::vector<GURL> foreign_fetch_scopes_;
   std::vector<url::Origin> foreign_fetch_origins_;
-  bool has_fetch_handler_ = true;
+  base::Optional<bool> has_fetch_handler_;
 
   Status status_ = NEW;
   std::unique_ptr<EmbeddedWorkerInstance> embedded_worker_;