Remove a deprecated wstring ToLower function.

views/controls/menu/menu_item_view.cc

Index: views/controls/menu/menu_item_view.cc
diff --git a/views/controls/menu/menu_item_view.cc b/views/controls/menu/menu_item_view.cc
index b88fc5b9b0c7a146fd4a8d586307c86044493d67..e0ca73d1f1abee6b3b0f722bb4912b6c4512db3b 100644
--- a/views/controls/menu/menu_item_view.cc
+++ b/views/controls/menu/menu_item_view.cc
@@ -5,6 +5,7 @@
 #include "views/controls/menu/menu_item_view.h"
 
 #include "app/l10n_util.h"
+#include "base/utf_string_conversions.h"
 #include "gfx/canvas.h"
 #include "grit/app_strings.h"
 #include "views/controls/button/text_button.h"
@@ -316,7 +317,7 @@ wchar_t MenuItemView::GetMnemonic() {
     if (index != std::wstring::npos) {
       if (index + 1 != title.size() && title[index + 1] != '&') {
         wchar_t char_array[1] = { title[index + 1] };
-        return l10n_util::ToLower(char_array)[0];
+        return UTF16ToWide(l10n_util::ToLower(WideToUTF16(char_array)))[0];
       }
       index++;
     }