Introduce background.scripts feature for extension manifests.

chrome/browser/extensions/extension_event_router.cc

Index: chrome/browser/extensions/extension_event_router.cc
diff --git a/chrome/browser/extensions/extension_event_router.cc b/chrome/browser/extensions/extension_event_router.cc
index d2f117917b01f781a275a8830d8a0459b8e756c7..f18ec663008acc3cd93a078f30d87d1040a91d6a 100644
--- a/chrome/browser/extensions/extension_event_router.cc
+++ b/chrome/browser/extensions/extension_event_router.cc
@@ -224,10 +224,10 @@ bool ExtensionEventRouter::CanDispatchEventNow(
 
   const Extension* extension = profile_->GetExtensionService()->
       GetExtensionById(extension_id, false);  // exclude disabled extensions
-  if (extension && extension->background_url().is_valid()) {
+  if (extension && extension->has_background_page()) {
     ExtensionProcessManager* pm = profile_->GetExtensionProcessManager();
     if (!pm->GetBackgroundHostForExtension(extension_id)) {
-      pm->CreateBackgroundHost(extension, extension->background_url());
+      pm->CreateBackgroundHost(extension, extension->GetBackgroundURL());
       return false;
     }
   }