[Hotword] Making enabling/disabling the setting enable/disable the hotword extension.

chrome/browser/search/hotword_service.h

Index: chrome/browser/search/hotword_service.h
diff --git a/chrome/browser/search/hotword_service.h b/chrome/browser/search/hotword_service.h
index d52bf4f875341874788323aafc675ac4f02b367a..c4383a51a45f3a00cadb13b24ded5073ad737a58 100644
--- a/chrome/browser/search/hotword_service.h
+++ b/chrome/browser/search/hotword_service.h
@@ -6,6 +6,7 @@
 #define CHROME_BROWSER_SEARCH_HOTWORD_SERVICE_H_
 
 #include "base/basictypes.h"
+#include "base/prefs/pref_change_registrar.h"
 #include "components/browser_context_keyed_service/browser_context_keyed_service.h"
 
 class Profile;
@@ -50,9 +51,19 @@ class HotwordService : public BrowserContextKeyedService {
   // already loaded successfully by some other means.
   virtual bool RetryHotwordExtension();
 
+  // Control the state of the hotword extension.
+  void DisableHotwordExtension();
+  void EnableHotwordExtension();
+
+  // Handles enabling/disabling the hotword extension when the user
+  // turns it off via the settings menu.
+  void OnHotwordSearchEnabledChanged(const std::string& pref_name);
+
  private:
   Profile* profile_;
 
+  PrefChangeRegistrar pref_registrar_;
+
   DISALLOW_COPY_AND_ASSIGN(HotwordService);
 };