🐳 Move linux pkg_config() calls into separate BUILD.gn files

build/config/linux/gconf/BUILD.gn

+# Copyright 2016 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/features.gni")
+import("//build/config/linux/pkg_config.gni")
+
+# CrOS doesn't install GTK, gconf or any gnome packages.
+assert(!is_chromeos && use_gconf)
+
+# These packages should _only_ be expected when building for a target.
+# If these extra checks are not run, gconf is required when building host
+# tools for a CrOS build.
+assert(current_toolchain == default_toolchain)
+
+pkg_config("gconf") {
+  packages = [ "gconf-2.0" ]
+  defines = [ "USE_GCONF" ]
+}