Introduce background.scripts feature for extension manifests.

chrome/browser/extensions/extension_service.cc

Index: chrome/browser/extensions/extension_service.cc
diff --git a/chrome/browser/extensions/extension_service.cc b/chrome/browser/extensions/extension_service.cc
index 655a80e55a9d6669924735bc2da54b64eea1c382..90920de29ea7f128bdd93c296e1652e1506aba25 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -2474,12 +2474,12 @@ ExtensionIdSet ExtensionService::GetAppIds() const {
 }
 
 bool ExtensionService::IsBackgroundPageReady(const Extension* extension) {
-  return (extension->background_url().is_empty() ||
+  return (!extension->has_background_page() ||
           extension_runtime_data_[extension->id()].background_page_ready);
 }
 
 void ExtensionService::SetBackgroundPageReady(const Extension* extension) {
-  DCHECK(!extension->background_url().is_empty());
+  DCHECK(extension->has_background_page());
   extension_runtime_data_[extension->id()].background_page_ready = true;
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_EXTENSION_BACKGROUND_PAGE_READY,