Move BookmarkIndex into bookmarks namespace.

components/bookmarks/browser/bookmark_index.h

Index: components/bookmarks/browser/bookmark_index.h
diff --git a/components/bookmarks/browser/bookmark_index.h b/components/bookmarks/browser/bookmark_index.h
index fed0ab3e5931588e755f4bcbc11bc012084be94b..08c73e0e8c6f1414d514c7a13c586c19a17b66a0 100644
--- a/components/bookmarks/browser/bookmark_index.h
+++ b/components/bookmarks/browser/bookmark_index.h
@@ -18,6 +18,8 @@ class BookmarkClient;
 class BookmarkNode;
 struct BookmarkMatch;
 
+namespace bookmarks {
+
 // BookmarkIndex maintains an index of the titles and URLs of bookmarks for
 // quick look up. BookmarkIndex is owned and maintained by BookmarkModel, you
 // shouldn't need to interact directly with BookmarkIndex.
@@ -117,4 +119,6 @@ class BookmarkIndex {
   DISALLOW_COPY_AND_ASSIGN(BookmarkIndex);
 };
 
+}  // namespace bookmarks
+
 #endif  // COMPONENTS_BOOKMARKS_BROWSER_BOOKMARK_INDEX_H_