a11y: add a11y title for bookmark chevron / "off the side button"

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

Index: chrome/browser/ui/cocoa/bookmarks/bookmark_button_cell.mm
diff --git a/chrome/browser/ui/cocoa/bookmarks/bookmark_button_cell.mm b/chrome/browser/ui/cocoa/bookmarks/bookmark_button_cell.mm
index 51750aee4547586cafd743b3ef439a5a06348416..9c1dd58e4a23f19d72e143276491ca723b9e41d1 100644
--- a/chrome/browser/ui/cocoa/bookmarks/bookmark_button_cell.mm
+++ b/chrome/browser/ui/cocoa/bookmarks/bookmark_button_cell.mm
@@ -40,6 +40,9 @@ const int kDefaultFontSize = 12;
 };  // namespace
 
 @interface OffTheSideButtonCell : BookmarkButtonCell
+
+- (NSString*)accessibilityTitle;
+
 @end
 @implementation OffTheSideButtonCell
 
@@ -47,6 +50,10 @@ const int kDefaultFontSize = 12;
   return YES;
 }
 
+- (NSString*)accessibilityTitle {
+  return l10n_util::GetNSString(IDS_ACCNAME_BOOKMARKS_CHEVRON);
+}
+
 @end
 
 @interface BookmarkButtonCell(Private)