content: convert zoom notifications to observer usage

chrome/browser/ui/zoom/zoom_controller.cc

Index: chrome/browser/ui/zoom/zoom_controller.cc
diff --git a/chrome/browser/ui/zoom/zoom_controller.cc b/chrome/browser/ui/zoom/zoom_controller.cc
index 24b33baad649d27d4287532503a79d6d1ad08c83..5b5430637731c8c43043acf6fe2432cee7031d10 100644
--- a/chrome/browser/ui/zoom/zoom_controller.cc
+++ b/chrome/browser/ui/zoom/zoom_controller.cc
@@ -22,7 +22,9 @@
 DEFINE_WEB_CONTENTS_USER_DATA_KEY(ZoomController);
 
 ZoomController::ZoomController(content::WebContents* web_contents)
-    : content::WebContentsObserver(web_contents),
+    : content::HostZoomMap::Observer(content::HostZoomMap::GetForBrowserContext(
+                                         web_contents->GetBrowserContext())),
+      content::WebContentsObserver(web_contents),
       zoom_percent_(100),
       observer_(NULL) {
   Profile* profile =
@@ -32,11 +34,6 @@ ZoomController::ZoomController(content::WebContents* web_contents)
                                       base::Unretained(this),
                                       std::string()));
 
-  content::HostZoomMap* zoom_map =
-      content::HostZoomMap::GetForBrowserContext(profile);
-  registrar_.Add(this, content::NOTIFICATION_ZOOM_LEVEL_CHANGED,
-                 content::Source<content::HostZoomMap>(zoom_map));
-
   UpdateState(std::string());
 }
 
@@ -59,6 +56,10 @@ int ZoomController::GetResourceForZoomLevel() const {
   return zoom > default_zoom_level_.GetValue() ? IDR_ZOOM_PLUS : IDR_ZOOM_MINUS;
 }
 
+void ZoomController::OnZoomLevelChanged(const std::string& host) {
+  UpdateState(host);
+}
+
 void ZoomController::DidNavigateMainFrame(
     const content::LoadCommittedDetails& details,
     const content::FrameNavigateParams& params) {
@@ -67,13 +68,6 @@ void ZoomController::DidNavigateMainFrame(
   UpdateState(std::string());
 }
 
-void ZoomController::Observe(int type,
-                             const content::NotificationSource& source,
-                             const content::NotificationDetails& details) {
-  DCHECK_EQ(content::NOTIFICATION_ZOOM_LEVEL_CHANGED, type);
-  UpdateState(*content::Details<std::string>(details).ptr());
-}
-
 void ZoomController::UpdateState(const std::string& host) {
   // TODO(dbeam): I'm not totally sure why this is happening, and there's been a
   // bit of effort to understand with no tangible results yet. It's possible