[omnibox mac] Make command-shift-enter open tab in foreground

Currently the code falls through to "if (command) then open in
background." This change breaks out the variation if shift is
also pressed.

Bug: 870789
Change-Id: Ie96d355c7c75bec276ed5322aac03f0d3f472a9b
Reviewed-on: https://chromium-review.googlesource.com/1170860Reviewed-by: Tommy Li <tommycli@chromium.org>
Commit-Queue: Kevin Bailey <krb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582268}

chrome/browser/ui/views/omnibox/omnibox_view_views.cc

@@ -1230,7 +1230,7 @@ bool OmniboxViewViews::HandleKeyEvent(views::Textfield* textfield,
               OmniboxPopupModel::TAB_SWITCH) {
         popup_view_->OpenMatch(WindowOpenDisposition::SWITCH_TO_TAB);
       } else {
-        if (alt) {
+        if (alt || (shift && command)) {
           model()->AcceptInput(WindowOpenDisposition::NEW_FOREGROUND_TAB,
                                false);
         } else if (command) {