Add MB config and installer target for an official CrOS builder.

chrome/installer/BUILD.gn

 # Copyright 2015 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/chrome_build.gni")
 
 declare_args() {
-  enable_linux_installer = is_desktop_linux && is_chrome_branded
+  enable_linux_installer = is_linux && is_chrome_branded
 }
 
 # Meta-target that forwards to the installer of the correct type (if any).
 group("installer") {
   if (enable_linux_installer) {
     deps = [
       "//chrome/installer/linux",
     ]
   }
 
   if (is_mac) {
     deps = [
       "//chrome/installer/mac",
     ]
   }
 }