Show a separator in the combobox of Bookmark Bubble.

There should be a separator in folder popup button to differenciate "Choose another folder"
button from already available bookmark folders.

BUG=237697

R=asvitkine@chromium.org

Review URL: https://codereview.chromium.org/463093002

Cr-Commit-Position: refs/heads/master@{#289033}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289033 0039d316-1c4b-4281-b951-d872f2087c98

chrome/browser/ui/cocoa/bookmarks/bookmark_bubble_controller.mm

@@ -332,6 +332,7 @@ using base::UserMetricsAction;
          toPopUpButton:folderPopUpButton_
            indentation:0];
   NSMenu* menu = [folderPopUpButton_ menu];
+  [menu addItem:[NSMenuItem separatorItem]];
   NSString* title = [[self class] chooseAnotherFolderString];
   NSMenuItem *item = [menu addItemWithTitle:title
                                      action:NULL