Provide a way to disable libpci dependency.

build/config/ui.gni

 # 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.
 
 # This file contains UI-related build flags. It should theoretically be in the
 # src/ui directory and only things that depend on the ui module should get the
 # definitions.
 #
 # However, today we have many "bad" dependencies on some of these flags from,
 # e.g. base, so they need to be global.
 #
 # See also build/config/features.gni
 
 declare_args() {
   # Indicates if Ash is enabled. Ash is the Aura Shell which provides a
   # desktop-like environment for Aura. Requires use_aura = true
   use_ash = is_win || is_linux
 
   # Indicates if Ozone is enabled. Ozone is a low-level library layer for Linux
   # that does not require X11.
   use_ozone = false
 
+  # Use the PCI lib to collect GPU information.

[brettw, 2014/10/30 17:00:50]

Can this comment include whether this is Linux only? (I assume it is).

Is it possible to move this to the BUILD.gn file in GPU? In the GN build we
avoid globals, and basically all of the stuff in ui.gni and features.gni should
be moved out.

+  use_libpci = true
+
   # Support ChromeOS touchpad gestures with ozone.
   use_evdev_gestures = false
 
   # Indicates if Aura is enabled. Aura is a low-level windowing library, sort
   # of a replacement for GDI or GTK.
   use_aura = is_win || is_linux
 
   # XInput2 multitouch support. Zero means disabled, nonzero indicates the
   # minimum XI2 version. For example, use_xi2_mt=2 means XI2.2 or above.
   use_xi2_mt = 2
@@ skipping 25 matching lines @@
 
 use_ozone_evdev = use_ozone
 
 use_glib = is_linux && !use_ozone
 
 use_clipboard_aurax11 = is_linux && use_aura && use_x11
 
 use_athena = false
 
 enable_hidpi = is_mac || is_chromeos || is_win