content: convert zoom notifications to observer usage

chrome/browser/profiles/off_the_record_profile_impl.cc

Index: chrome/browser/profiles/off_the_record_profile_impl.cc
diff --git a/chrome/browser/profiles/off_the_record_profile_impl.cc b/chrome/browser/profiles/off_the_record_profile_impl.cc
index 489c2aec63836e5c08735aabc07ae084d1f52ff8..23f3ff04d37f05d731fbf6085a9f6d4e71db9c59 100644
--- a/chrome/browser/profiles/off_the_record_profile_impl.cc
+++ b/chrome/browser/profiles/off_the_record_profile_impl.cc
@@ -45,8 +45,6 @@
 #include "chrome/common/render_messages.h"
 #include "content/public/browser/browser_thread.h"
 #include "content/public/browser/host_zoom_map.h"
-#include "content/public/browser/notification_service.h"
-#include "content/public/browser/notification_types.h"
 #include "content/public/browser/render_process_host.h"
 #include "content/public/browser/storage_partition.h"
 #include "content/public/browser/web_contents.h"
@@ -165,8 +163,7 @@ void OffTheRecordProfileImpl::InitHostZoomMap() {
   host_zoom_map->CopyFrom(parent_host_zoom_map);
   // Observe parent's HZM change for propagating change of parent's
   // change to this HZM.
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                 content::Source<HostZoomMap>(parent_host_zoom_map));
+  Observe(parent_host_zoom_map);
 }
 
 #if defined(OS_ANDROID)
@@ -428,21 +425,15 @@ GURL OffTheRecordProfileImpl::GetHomePage() {
   return profile_->GetHomePage();
 }
 
-void OffTheRecordProfileImpl::Observe(
-    int type,
-    const content::NotificationSource& source,
-    const content::NotificationDetails& details) {
-  if (type == content::NOTIFICATION_ZOOM_LEVEL_CHANGED) {
-    const std::string& host =
-        *(content::Details<const std::string>(details).ptr());
-    if (!host.empty()) {
-      HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
-      HostZoomMap* parent_host_zoom_map =
-          HostZoomMap::GetForBrowserContext(profile_);
-      double level = parent_host_zoom_map->GetZoomLevel(host);
-      host_zoom_map->SetZoomLevel(host, level);
-    }
-  }
+void OffTheRecordProfileImpl::OnZoomLevelChanged(const std::string& host) {
+  if (host.empty())
+    return;
+
+  HostZoomMap* host_zoom_map = HostZoomMap::GetForBrowserContext(this);
+  HostZoomMap* parent_host_zoom_map =
+      HostZoomMap::GetForBrowserContext(profile_);
+  double level = parent_host_zoom_map->GetZoomLevel(host);
+  host_zoom_map->SetZoomLevel(host, level);
 }
 
 #if defined(OS_CHROMEOS)