Improve FaviconHandler tests by testing public API

components/favicon/core/BUILD.gn

 # Copyright 2014 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.
 
 static_library("core") {
   sources = [
     "fallback_url_util.cc",
     "fallback_url_util.h",
     "favicon_client.h",
     "favicon_driver.cc",
@@ skipping 42 matching lines @@
   sources = [
     "fallback_url_util_unittest.cc",
     "favicon_handler_unittest.cc",
     "favicon_service_impl_unittest.cc",
     "large_icon_service_unittest.cc",
   ]
 
   deps = [
     ":core",
     "//base",
+    "//base/test:test_support",
     "//components/favicon/core/test:test_support",
     "//components/favicon_base",
     "//components/history/core/browser:browser",
     "//components/history/core/test:test",
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
     "//ui/base",
     "//ui/gfx",
     "//ui/gfx:test_support",
     "//url",
   ]
 }