[Chromecast] Consolidate duplicated crash test functions.

chromecast/app/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("//testing/test.gni")
 
 source_set("cast_crash_client") {
   sources = [
     "android/cast_crash_reporter_client_android.cc",
     "android/cast_crash_reporter_client_android.h",
@@ skipping 18 matching lines @@
   sources = [
     "linux/cast_crash_reporter_client_unittest.cc",
   ]
 
   deps = [
     ":cast_crash_client",
     "//base",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//chromecast/crash",
+    "//chromecast/crash:cast_crash_test_support",
     "//testing/gtest",
   ]
 }