Add a snapshot of flutter/engine/src/build to our sdk

build/config/linux/gtk/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/gtk to use GTK.
+#
+# 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("gtk_internal_config") {
+  # Gtk requires gmodule, but it does not list it as a dependency in some
+  # misconfigured systems.
+  packages = [
+    "gmodule-2.0",
+    "gtk+-2.0",
+    "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("gtk") {
+  visibility = [
+    "//chrome/browser/ui/libgtk2ui",
+    "//gpu/gles2_conform_support:gles2_conform_test_windowless",
+    "//remoting/host",
+    "//remoting/host/it2me:remote_assistance_host",
+    "//remoting/host:remoting_me2me_host_static",
+  ]
+  public_configs = [ ":gtk_internal_config" ]
+}
+
+# Depend on "gtkprint" to get this.
+pkg_config("gtkprint_internal_config") {
+  packages = [ "gtk+-unix-print-2.0" ]
+}
+
+group("gtkprint") {
+  visibility = [ "//chrome/browser/ui/libgtk2ui" ]
+  public_configs = [ ":gtkprint_internal_config" ]
+}