Fix uninitialized memory introduced in https://codereview.chromium.org/623823002/

BUG=383125
TBR=michaeln

Review URL: https://codereview.chromium.org/676963002

Cr-Commit-Position: refs/heads/master@{#301059}

content/common/service_worker/service_worker_types.cc

@@ -73,6 +73,8 @@ ServiceWorkerObjectInfo::ServiceWorkerObjectInfo()
       state(blink::WebServiceWorkerStateUnknown) {}
 
 ServiceWorkerRegistrationObjectInfo::ServiceWorkerRegistrationObjectInfo()
-    : handle_id(kInvalidServiceWorkerRegistrationHandleId) {}
+    : handle_id(kInvalidServiceWorkerRegistrationHandleId),
+      registration_id(kInvalidServiceWorkerRegistrationId) {
+}
 
 }  // namespace content