[mac][omnibox] Hide speech submenu in omnibox when no text is selected

This CL modifies the context menu behavior to match the new speech
submenu behavior on the New Tab Page.

Bug: 1141372
Change-Id: Icb79a66290d1c49b132ce0bef123a91facf7d67c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2500423Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Commit-Queue: Angela Yoeurng <yoangela@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821328}

ui/views/controls/views_text_services_context_menu_mac.mm

@@ -68,9 +68,10 @@ ViewsTextServicesContextMenuMac::ViewsTextServicesContextMenuMac(
     menu->InsertItemAt(
         0, IDS_CONTENT_CONTEXT_LOOK_UP,
         l10n_util::GetStringFUTF16(IDS_CONTENT_CONTEXT_LOOK_UP, text));
+
+    text_services_menu_.AppendToContextMenu(menu);
   }
 
-  text_services_menu_.AppendToContextMenu(menu);
   text_services_menu_.AppendEditableItems(menu);
 }