Unbundle libdrm

build/linux/unbundle/libdrm.gn

+# Copyright 2017 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")
+import("//build/shim_headers.gni")
+
+pkg_config("system_libdrm") {
+  packages = [ "libdrm" ]
+}
+
+shim_headers("libdrm_shim") {
+  root_path = "src/include"
+  headers = [ "drm.h" ]
+}
+
+source_set("libdrm") {
+  deps = [
+    ":libdrm_shim",
+  ]
+  public_configs = [ ":system_libdrm" ]
+}