omnibox: allow command-enter on all platforms

On macOS, Command-Enter is available via the ⌘ key, but Windows & Linux
can trigger this equivalent functionality via the Windows ⊞ key, and
Chrome OS has a search 🔍 key.  Support passing this disposition in the
omnibox on all platforms.

Bug: None
Change-Id: I9a477678abbb8b369bee0eb9352f769d6b5d8fd8
Reviewed-on: https://chromium-review.googlesource.com/1132102Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Reviewed-by: Justin Donnelly <jdonnelly@chromium.org>
Commit-Queue: Mike Frysinger <vapier@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573949}

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

@@ -1179,11 +1179,7 @@ bool OmniboxViewViews::HandleKeyEvent(views::Textfield* textfield,
   const bool shift = event.IsShiftDown();
   const bool control = event.IsControlDown();
   const bool alt = event.IsAltDown() || event.IsAltGrDown();
-#if defined(OS_MACOSX)
   const bool command = event.IsCommandDown();
-#else
-  const bool command = false;
-#endif
   switch (event.key_code()) {
     case ui::VKEY_RETURN:
       if (model()->popup_model()->SelectedLineHasTabMatch() &&