[Extensions] Remove unused observers from rules_monitor_service

The observer code was introduced in crrev.com/c/1139048 to detect rule
changes. However it seems that these observers were applicable only for
previous declarative APIs and not the declarative net request API,
where they remain unused.

Bug: 971455
Change-Id: Ie6a1c38d2ed11f9ce999f41c3b553fe0ad4e1a08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1648819
Commit-Queue: Kelvin Jiang <kelvinjiang@chromium.org>
Auto-Submit: Kelvin Jiang <kelvinjiang@chromium.org>
Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667311}

extensions/browser/api/declarative_net_request/rules_monitor_service.cc

@@ -181,16 +181,6 @@ bool RulesMonitorService::HasRegisteredRuleset(
          extensions_with_rulesets_.end();
 }
 
-void RulesMonitorService::AddObserver(Observer* observer) {
-  DCHECK(observer);
-  observers_.AddObserver(observer);
-}
-
-void RulesMonitorService::RemoveObserver(Observer* observer) {
-  DCHECK(observer);
-  observers_.RemoveObserver(observer);
-}
-
 void RulesMonitorService::UpdateDynamicRules(
     const Extension& extension,
     std::vector<api::declarative_net_request::Rule> rules,
@@ -380,8 +370,6 @@ void RulesMonitorService::OnRulesetLoaded(LoadRequestData load_data) {
     return;
 
   extensions_with_rulesets_.insert(load_data.extension_id);
-  for (auto& observer : observers_)
-    observer.OnRulesetLoaded();
 
   base::OnceClosure load_ruleset_on_io =
       base::BindOnce(&LoadRulesetOnIOThread, load_data.extension_id,

extensions/browser/api/declarative_net_request/rules_monitor_service.h

@@ -46,15 +46,6 @@ struct LoadRequestData;
 class RulesMonitorService : public BrowserContextKeyedAPI,
                             public ExtensionRegistryObserver {
  public:
-  class Observer {
-   public:
-    // Called when this service loads a new ruleset.
-    virtual void OnRulesetLoaded() = 0;
-
-   protected:
-    virtual ~Observer() {}
-  };
-
   // BrowserContextKeyedAPI implementation.
   static BrowserContextKeyedAPIFactory<RulesMonitorService>*
   GetFactoryInstance();
@@ -65,10 +56,6 @@ class RulesMonitorService : public BrowserContextKeyedAPI,
   // the given |extension_id|.
   bool HasRegisteredRuleset(const ExtensionId& extension_id) const;
 
-  // Adds or removes an observer.
-  void AddObserver(Observer* observer);
-  void RemoveObserver(Observer* observer);
-
   // Updates the dynamic rules for the |extension| and then invokes
   // |callback| with an optional error.
   using DynamicRuleUpdateUICallback =
@@ -125,8 +112,6 @@ class RulesMonitorService : public BrowserContextKeyedAPI,
   ExtensionRegistry* const extension_registry_;
   WarningService* const warning_service_;
 
-  base::ObserverList<Observer>::Unchecked observers_;
-
   content::BrowserContext* const context_;
 
   // Must be the last member variable. See WeakPtrFactory documentation for