service worker: Add NavigationPreload runtime flag and skeleton interface

third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp

Index: third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
diff --git a/third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp b/third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
index 502b61e5b19bce95902c8a752f2a6e8e7b4f685c..57960776842873353b831d33df49b2993edd38d1 100644
--- a/third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
+++ b/third_party/WebKit/Source/modules/serviceworkers/ServiceWorkerRegistration.cpp
@@ -74,6 +74,12 @@ ServiceWorkerRegistration* ServiceWorkerRegistration::getOrCreate(
   return newRegistration;
 }
 
+NavigationPreloadManager* ServiceWorkerRegistration::navigationPreload() {
+  if (!m_navigationPreload)
+    m_navigationPreload = NavigationPreloadManager::create();
+  return m_navigationPreload;
+}
+
 String ServiceWorkerRegistration::scope() const {
   return m_handle->registration()->scope().string();
 }
@@ -142,6 +148,7 @@ DEFINE_TRACE(ServiceWorkerRegistration) {
   visitor->trace(m_installing);
   visitor->trace(m_waiting);
   visitor->trace(m_active);
+  visitor->trace(m_navigationPreload);
   EventTargetWithInlineData::trace(visitor);
   ActiveDOMObject::trace(visitor);
   Supplementable<ServiceWorkerRegistration>::trace(visitor);