[Chromecast] Enable MultizoneBackendTest on Earth.

chromecast/media/cma/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//chromecast/chromecast.gni")
 import("//testing/test.gni")
 
 # Targets may depend on this to bring in every CMA component.
 group("cma") {
   public_deps = [
@@ skipping 56 matching lines @@
     "//media",
     "//testing/gmock",
     "//testing/gtest",
   ]
 
   data = [
     "//media/test/data/",
   ]
 
   # MultizoneBackendTest verifies rendering delay reported by the backend.
-  # Since rendering delay is optional on video platforms, enable this test
-  # on audio devices only.
-  if (is_cast_audio_only && !is_cast_desktop_build) {
+  if (supports_multizone) {
     sources += [ "backend/multizone_backend_unittest.cc" ]
   }
 }