Sync more GN unit tests with GYP.

components/favicon/content/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.
 
-static_library("content") {
+source_set("content") {
   sources = [
     "content_favicon_driver.cc",
     "content_favicon_driver.h",
     "favicon_url_util.cc",
     "favicon_url_util.h",
   ]
 
+  public_deps = [
+    "//ui/gfx",
+  ]
   deps = [
     "//base",
     "//components/favicon/core",
     "//components/favicon_base",
     "//content/public/browser",
     "//content/public/common",
-    "//ui/gfx",
   ]
 }
+
+source_set("unit_tests") {
+  testonly = true
+  sources = [
+    "content_favicon_driver_unittest.cc",
+  ]
+  deps = [
+    ":content",
+    "//content/public/browser",
+    "//testing/gtest",
+  ]
+}