bookmarks: Move BookmarkModelObserver into 'bookmarks' namespace.

chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h

Index: chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h
diff --git a/chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h b/chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h
index 97dc4a1339deb6c0a62bd904954f54892c586f6b..407597ac45b7ef2ef5515b80efb7f9202da1f3ba 100644
--- a/chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h
+++ b/chrome/browser/ui/cocoa/bookmarks/bookmark_menu_bridge.h
@@ -33,13 +33,13 @@ class Profile;
 @class NSMenuItem;
 @class BookmarkMenuCocoaController;
 
-class BookmarkMenuBridge : public BookmarkModelObserver,
+class BookmarkMenuBridge : public bookmarks::BookmarkModelObserver,
                            public MainMenuItem {
  public:
   BookmarkMenuBridge(Profile* profile, NSMenu* menu);
   ~BookmarkMenuBridge() override;
 
-  // BookmarkModelObserver:
+  // bookmarks::BookmarkModelObserver:
   void BookmarkModelLoaded(BookmarkModel* model, bool ids_reassigned) override;
   void BookmarkModelBeingDeleted(BookmarkModel* model) override;
   void BookmarkNodeMoved(BookmarkModel* model,