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 597188fe8c6fd1b484503e199ab51b8bc6188eda..60142185155d51dbf45a10763bc363c730a0f74a 100644
--- a/chrome/browser/extensions/extension_service.cc
+++ b/chrome/browser/extensions/extension_service.cc
@@ -2478,12 +2478,12 @@ 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,