Flip Linux ChromeOS trybot to GN

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.
 
 # This is the root build file for GN. GN will start processing by loading this
 # file, and recursively load all dependencies until all dependencies are either
 # resolved or known not to exist (which will cause the build to fail). So if
 # you add a new build file, there must be some path of dependencies from this
 # file to your new one or GN won't know about it.
 
@@ skipping 858 matching lines @@
     if (is_win) {
       deps += [
         # "//gpu:angle_perftests", TODO(GYP): crbug.com/537008
       ]
     } else {
       deps += [ "//breakpad:minidump_stackwalk($host_toolchain)" ]
     }
   }
 }
 
+# For compatibility with GYP. The linux_chromium_chromeos_rel_ng and
+# linux_chromium_chromeos_compile_rel_ng bots reference this target as
+# something to build, but all targets for those bots to compile are set
+# up differently.
+# TODO bug 601920: Remove reference to aura_builder on bot config and delete
+# this group.
+group("aura_builder") {
+}
+
 # Because of the source assignment filter, many targets end up over-filtering
 # their sources if the output directory contains a platform name. Assert that
 # this doesn't happen. http://crbug.com/548283
 template("assert_valid_out_dir") {
   # List copied from //build/config/BUILDCONFIG.gn.
   set_sources_assignment_filter([
                                   "*\bandroid/*",
                                   "*\bchromeos/*",
                                   "*\bcocoa/*",
                                   "*\bios/*",
                                   "*\blinux/*",
                                   "*\bmac/*",
                                   "*\bposix/*",
                                   "*\bwin/*",
                                 ])
   assert(target_name != "")  # Mark as used.
   sources = invoker.actual_sources
   assert(
       sources == invoker.actual_sources,
       "Do not use a platform name in your output directory (found \"$root_build_dir\"). http://crbug.com/548283")
 }
 
 assert_valid_out_dir("_unused") {
   actual_sources = [ "$root_build_dir/foo" ]
 }