views: Enable toolkit_views on Cast Fuchsia

This is already in use as evidenced by the build failures
in https://chromium-review.googlesource.com/c/chromium/src/+/1918654.

Enable it so the //ui/views build file can verify toolkit_views=true,
which will help diagnose invalid dependencies on platforms that don't
intend to use views (such as Chromecast Android).

Bug: 1021770

Change-Id: Iefef6bf25f26d50ac6e871bc17c96b1ba74b3c97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946850
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Reviewed-by: Wez <wez@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#721164}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 8c240c45a41efadbd4f6b267d41bcd4f7e80a378

config/ui.gni

@@ -32,7 +32,7 @@ declare_args() {
 
 declare_args() {
   # True means the UI is built using the "views" framework.
-  toolkit_views = (is_mac || is_win || is_chromeos || use_aura) && !is_fuchsia
+  toolkit_views = is_mac || is_win || is_linux || (is_fuchsia && is_chromecast)
 
   # Whether we should use glib, a low level C utility library.
   use_glib = is_linux && !use_ozone