headless: Add gn settings for embedded build and headless mode

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 (see features.gni for Chrome
 # feature-related ones). These should theoretically be moved to the ui
 # directory.
 #
 # However, today we have many "bad" dependencies on some of these flags from,
 # e.g. base, so they need to be global to match the GYP configuration. Also,
 # anything that needs a grit define must be in either this file or features.gni.
 #
 # PLEASE TRY TO AVOID ADDING FLAGS TO THIS FILE in cases where grit isn't
 # required. See the declare_args block of BUILDCONFIG.gn for advice on how
 # to set up feature flags.
 
 import("//build/config/chromecast_build.gni")
+import("//build/config/headless_build.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) && !is_chromecast
+  use_ash = (is_win || is_linux) && !is_chromecast && !is_headless

[jam, 2015/10/26 17:05:31]

curious, why?

[Sami, 2015/10/26 18:09:06]

Is there a reason why we'd want to have a full desktop shell when running
headless? It would seem like window decorations etc. would just get in the way?

[jam, 2015/10/30 16:15:49]

good point, ok

 
   # Indicates if Ozone is enabled. Ozone is a low-level library layer for Linux
   # that does not require X11. Enabling this feature disables use of glib, x11,
   # Pango, and Cairo. Default to false on non-Chromecast builds.
-  use_ozone = is_chromecast && !is_android
+  use_ozone = (is_chromecast || is_headless) && !is_android
 
   # 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 || is_chromecast
+  use_aura = is_win || is_linux || is_chromecast || is_headless

[jam, 2015/10/26 17:05:31]

is this really necessary? i.e. you're targeting linux for now right?

[Sami, 2015/10/26 18:09:06]

Yes, but don't you need to enable Aura to be able to use Ozone in the first
place?

[jam, 2015/10/30 16:15:49]

if so, then this should key off ozone. but ozone is only on linux, so really
it's by definition that aura is on (i.e. no need for changes to this line)

[Sami, 2015/11/05 19:08:17]

Ah, got it, is_linux should be enough. Removed.

 
   # True means the UI is built using the "views" framework.
-  toolkit_views =
-      (is_mac || is_win || is_chromeos || use_aura) && !is_chromecast
+  toolkit_views = (is_mac || is_win || is_chromeos || use_aura) &&
+                  !is_chromecast && !is_headless

[jam, 2015/10/26 17:05:31]

curious why?

[Sami, 2015/10/26 18:09:06]

Similarly to disabling ash, this gets rid of browser chrome which I don't think
we need.

[jam, 2015/10/30 16:15:49]

if the ui isn't built using views, then which toolkit is used? i think what you
really want is not to build any UI code. but this is changing the toolkit.. i.e.
i'm worried that this introduces another platform to support: linux without
views.

[Sami, 2015/11/05 19:08:17]

We've explored this a little more now and I think you're right: the gyp
equivalent this was copied from was there only because they wanted to build a
stripped down version of Content Shell which didn't use Views. Since we're not
going to use Content Shell, there's no need for this setting either. Removed.

 
   # Whether the entire browser uses toolkit-views on Mac instead of Cocoa.
   mac_views_browser = false
 
   # Whether we should use GTKv3 instead of GTKv2.
   use_gtk3 = false
 
   # Optional system libraries.
   use_xkbcommon = false
 }
@@ skipping 23 matching lines @@
 }
 
 # Whether to use atk, the Accessibility ToolKit library
 use_atk = is_desktop_linux && use_x11
 
 use_clipboard_aurax11 = is_linux && use_aura && use_x11
 
 enable_hidpi = is_mac || is_win || is_linux
 
 enable_topchrome_md = is_chromeos || is_win || is_linux