headless: Replace is_headless gn setting with an args template

net/BUILD.gn

 # Copyright (c) 2013 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/buildflag_header.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/crypto.gni")
 import("//build/config/features.gni")
 import("//build/config/ui.gni")
@@ skipping 10 matching lines @@
 } else if (is_mac) {
   import("//build/config/mac/mac_sdk.gni")
 }
 
 # The list of net files is kept in net.gypi. Read it.
 gypi_values = exec_script("//build/gypi_to_gn.py",
                           [ rebase_path("net.gypi") ],
                           "scope",
                           [ "net.gypi" ])
 
-# Disable Kerberos on ChromeOS, iOS, Chromecast and headless, at least for now.
-# It needs configuration (krb5.conf and so on).
-use_kerberos = !is_chromeos && !is_ios && !is_chromecast && !is_headless
-
 # The way the cache uses mmap() is inefficient on some Android devices. If
 # this flag is set, we hackily avoid using mmap() in the disk cache. We are
 # pretty confident that mmap-ing the index would not hurt any existing x86
 # android devices, but we cannot be so sure about the variety of ARM devices.
 # So enable it for x86 only for now.
 posix_avoid_mmap = is_android && current_cpu != "x86"
 
 use_v8_in_net = !is_ios
 enable_built_in_dns = !is_ios
 
 declare_args() {
   # Disables support for file URLs.  File URL support requires use of icu.
   disable_file_support = false
 
   # WebSockets and socket stream code are not used on iOS and are optional in
   # cronet.
   enable_websockets = !is_ios
   disable_ftp_support = is_ios
+
+  # Disable Kerberos on ChromeOS, iOS, Chromecast, at least for now.
+  # It needs configuration (krb5.conf and so on).

[asanka, 2016/03/31 17:48:06]

Nit: Comments in declare_args() are used to describe the option and show up in
'gn args --list' output. In this case the comment should describe what
'use_kerberos' does and optionally explain the requirements for setting it to
true.

[Sami, 2016/03/31 17:56:38]

Good point. I've clarified the comment (to the best of my understanding).

+  use_kerberos = !is_chromeos && !is_ios && !is_chromecast
 }
 
 config("net_config") {
   defines = []
   if (posix_avoid_mmap) {
     defines += [ "POSIX_AVOID_MMAP" ]
   }
   if (disable_file_support) {
     defines += [ "DISABLE_FILE_SUPPORT" ]
   }
@@ skipping 1866 matching lines @@
 fuzzer_test("net_quic_crypto_framer_parse_message_fuzzer") {
   sources = [
     "quic/quic_crypto_framer_parse_message_fuzzer.cc",
   ]
   deps = [
     ":net_fuzzer_test_support",
     "//base",
     "//net",
   ]
 }