[chromecast] Enables cma tests if is_cast_using_cma_backend.

chromecast/media/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("//media/media_options.gni")
 import("//testing/test.gni")
 
 group("media") {
   public_deps = [
@@ skipping 26 matching lines @@
     "//chromecast/base/metrics:test_support",
     "//chromecast/media/cma:test_support",
     "//chromecast/public",
     "//media",
     "//media/audio:test_support",
     "//media/base:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 
-  if (!is_android) {
+  if (is_cast_using_cma_backend) {
     deps += [ "//chromecast/media/cma:unittests" ]
+    if (is_android) {
+      shard_timeout = 300
+    }
   }
 }