Gtk3 ui: Add libgtk3ui as a separate build component

build/config/linux/gtk3/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("//build/config/linux/pkg_config.gni")
 
 assert(is_linux, "This file should only be referenced on Linux")
 
 # Depend on //build/config/linux/gtk3 to use GTKv3.
 #
 # GN doesn't check visibility for configs so we give this an obviously internal
 # name to discourage random targets from accidentally depending on this and
 # bypassing the GTK target's visibility.
 pkg_config("gtk3_internal_config") {
   # Gtk requires gmodule, but it does not list it as a dependency in some
   # misconfigured systems.
   packages = [
     "gmodule-2.0",
     "gtk+-3.0",
     "gthread-2.0",
   ]
 }
 
 # Basically no parts of Chrome should depend on GTK. To prevent accidents, the
 # parts that explicitly need GTK are whitelisted on this target.
 group("gtk3") {
   visibility = [
-    "//chrome/browser/ui/libgtk2ui",
+    "//chrome/browser/ui/libgtkui:libgtk3ui",
     "//gpu/gles2_conform_support:gles2_conform_test_windowless",
     "//remoting/host",
     "//remoting/host/it2me:common",
     "//remoting/host/it2me:remote_assistance_host",
     "//remoting/host:remoting_me2me_host_static",
     "//remoting/test:it2me_standalone_host_main",
   ]
   public_configs = [ ":gtk3_internal_config" ]
 }
 
 # Depend on "gtkprint" to get this.
 pkg_config("gtkprint3_internal_config") {
   packages = [ "gtk+-unix-print-3.0" ]
 }
 
 group("gtkprint3") {
-  visibility = [ "//chrome/browser/ui/libgtk2ui" ]
+  visibility = [ "//chrome/browser/ui/libgtkui:libgtk3ui" ]
   public_configs = [ ":gtkprint3_internal_config" ]
 }