Add chrome test support target to GN build.

content/public/browser/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.
 
 import("//content/browser/browser.gni")
 import("//build/config/ui.gni")
 
 # See //content/BUILD.gn for how this works.
 group("browser") {
   if (is_component_build) {
     deps = [ "//content" ]
   } else {
     deps = [ ":browser_sources" ]
   }
   forward_dependent_configs_from = deps
 }
 
 source_set("browser_sources") {
-  visibility = [ "//content/*" ]
-
   if (is_ios) {
     # iOS doesn't get the normal file list and only takes these whitelisted
     # files.
     sources = [
       "browser_main_parts.cc",
       "content_browser_client.cc",
       "favicon_status.cc",
       "navigation_details.cc",
       "notification_registrar.cc",
       "page_navigator.cc",
@@ skipping 23 matching lines @@
   allow_circular_includes_from = [
     # This target is a pair with content/browser. They always go together and
     # include headers from each other.
     # TODO(brettw) enable this when this permits non-dependent targets.
     #"//content/browser",
   ]
 
   # We expose skia headers in the public API.
   forward_dependent_configs_from = [ "//skia" ]
 }