Added CHECKs for null pointers in ChromeAppSorting.

extensions/browser/null_app_sorting.cc

Index: extensions/browser/null_app_sorting.cc
diff --git a/extensions/browser/null_app_sorting.cc b/extensions/browser/null_app_sorting.cc
index 384f5b14a60c353e1bda3ecf42e0cdfe43f3071d..855de55dc4a124cc21176995fb2e4e082a1136b9 100644
--- a/extensions/browser/null_app_sorting.cc
+++ b/extensions/browser/null_app_sorting.cc
@@ -26,6 +26,9 @@ NullAppSorting::~NullAppSorting() {
 void NullAppSorting::SetExtensionScopedPrefs(ExtensionScopedPrefs* prefs) {
 }
 
+void NullAppSorting::CheckExtensionScopedPrefs() const {
+}
+
 void NullAppSorting::SetExtensionSyncService(
     ExtensionSyncService* extension_sync_service) {
 }