Implement WebPushProvider.unregister() in Chromium.

content/public/browser/push_messaging_service.h

Index: content/public/browser/push_messaging_service.h
diff --git a/content/public/browser/push_messaging_service.h b/content/public/browser/push_messaging_service.h
index fdc92f432d49789e98dab1c6136fc5e6e84a029a..8ccf69be341cd44d0f56aea9be2c05ae37d56b57 100644
--- a/content/public/browser/push_messaging_service.h
+++ b/content/public/browser/push_messaging_service.h
@@ -19,9 +19,10 @@ namespace content {
 // push messaging services like GCM. Must only be used on the UI thread.
 class CONTENT_EXPORT PushMessagingService {
  public:
-  typedef base::Callback<void(const std::string& /* registration_id */,
-                              PushRegistrationStatus /* status */)>
-      RegisterCallback;
+  using RegisterCallback =
+      base::Callback<void(const std::string& /* registration_id */,
+                          PushRegistrationStatus /* status */)>;
+  using UnregisterCallback = base::Callback<void(bool)>;
 
   virtual ~PushMessagingService() {}
 
@@ -64,6 +65,12 @@ class CONTENT_EXPORT PushMessagingService {
   virtual blink::WebPushPermissionStatus GetPermissionStatus(
       const GURL& requesting_origin,
       const GURL& embedding_origin) = 0;
+
+  // Unregister an origin and its associated service worker registration id from
+  // the push service.
+  virtual void Unregister(const GURL& requesting_origin,
+                          int64 service_worker_registration_id,
+                          const UnregisterCallback& callback) = 0;
 };
 
 }  // namespace content