Revert 170319 - Removed dead code from chrome/browser/extensions/api/declarative

chrome/browser/extensions/api/declarative/rules_registry_with_cache.cc

Index: chrome/browser/extensions/api/declarative/rules_registry_with_cache.cc
===================================================================
--- chrome/browser/extensions/api/declarative/rules_registry_with_cache.cc	(revision 170756)
+++ chrome/browser/extensions/api/declarative/rules_registry_with_cache.cc	(working copy)
@@ -20,6 +20,10 @@
     : delegate_(delegate) {
 }
 
+void RulesRegistryWithCache::AddReadyCallback(const base::Closure& callback) {
+  ready_callbacks_.push_back(callback);
+}
+
 void RulesRegistryWithCache::OnReady() {
   for (size_t i = 0; i < ready_callbacks_.size(); ++i)
     ready_callbacks_[i].Run();