Move BookmarkExpandedStateTracker into bookmarks namespace.

components/bookmarks/browser/bookmark_expanded_state_tracker.h

Index: components/bookmarks/browser/bookmark_expanded_state_tracker.h
diff --git a/components/bookmarks/browser/bookmark_expanded_state_tracker.h b/components/bookmarks/browser/bookmark_expanded_state_tracker.h
index 3bd86337c86faeeaa171569705a2c89c5a4ca0fe..6aadaf260135e69ec45c0b9937a75dc0fe549c78 100644
--- a/components/bookmarks/browser/bookmark_expanded_state_tracker.h
+++ b/components/bookmarks/browser/bookmark_expanded_state_tracker.h
@@ -13,6 +13,8 @@ class BookmarkModel;
 class BookmarkNode;
 class PrefService;
 
+namespace bookmarks {
+
 // BookmarkExpandedStateTracker is used to track a set of expanded nodes. The
 // nodes are persisted in preferences. If an expanded node is removed from the
 // model BookmarkExpandedStateTracker removes the node.
@@ -53,4 +55,6 @@ class BookmarkExpandedStateTracker : public BaseBookmarkModelObserver {
   DISALLOW_COPY_AND_ASSIGN(BookmarkExpandedStateTracker);
 };
 
+}  // namespace bookmarks
+
 #endif  // COMPONENTS_BOOKMARKS_BROWSER_BOOKMARK_EXPANDED_STATE_TRACKER_H_