bookmarks: Move BaseBookmarkModelObserver into 'bookmarks' namespace.

chrome/browser/undo/bookmark_undo_service.h

Index: chrome/browser/undo/bookmark_undo_service.h
diff --git a/chrome/browser/undo/bookmark_undo_service.h b/chrome/browser/undo/bookmark_undo_service.h
index 4d42b37a9d24cdce8074b1ec61f26b48fb7d8e59..944ea95a35bba56c87397cd8104c8c4229d4123a 100644
--- a/chrome/browser/undo/bookmark_undo_service.h
+++ b/chrome/browser/undo/bookmark_undo_service.h
@@ -22,7 +22,7 @@ class BookmarkUndoOperation;
 
 // BookmarkUndoService is owned by the profile, and is responsible for observing
 // BookmarkModel changes in order to provide an undo for those changes.
-class BookmarkUndoService : public BaseBookmarkModelObserver,
+class BookmarkUndoService : public bookmarks::BaseBookmarkModelObserver,
                             public KeyedService,
                             public BookmarkRenumberObserver {
  public:
@@ -32,7 +32,7 @@ class BookmarkUndoService : public BaseBookmarkModelObserver,
   UndoManager* undo_manager() { return &undo_manager_; }
 
  private:
-  // BaseBookmarkModelObserver:
+  // bookmarks::BaseBookmarkModelObserver:
   void BookmarkModelChanged() override {}
   void BookmarkModelLoaded(BookmarkModel* model, bool ids_reassigned) override;
   void BookmarkModelBeingDeleted(BookmarkModel* model) override;