chromecast: Fix link error in cast_accessibility_unittests

This fixes a link error for cast_accessibility_unittests when built with
chromecast_branding = "internal":

ld.lld: error: undefined symbol: chromecast::CreateSysInfo()

Bug: b/168243031
Change-Id: I90529de006b6a97a6f933591db8efe981e24621e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2405564Reviewed-by: Sean Topping <seantopping@chromium.org>
Commit-Queue: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#806023}

chromecast/browser/accessibility/flutter/BUILD.gn

@@ -38,6 +38,7 @@ test("cast_accessibility_unittests") {
     ":accessibility",
     "//base",
     "//base/test:run_all_unittests",
+    "//chromecast:cast_shell_lib",
     "//chromecast/browser",
     "//extensions/browser/api",
     "//skia",