Remove hotword installation code at compile time if hotwording disabled.

build/config/features.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 Chrome-feature-related build flags (see ui.gni for
 # UI-related ones). These should theoretically be moved to the build files of
 # the features themselves.
 #
 # 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,
@@ skipping 39 matching lines @@
   # --debug-devtools cmdline switch.
   debug_devtools = false
 
   # Enables WebRTC.
   # TODO(GYP) make mac work.
   enable_webrtc = !is_ios
 
   # Enables the Media Router.
   enable_media_router = !is_ios
 
+  # 'Ok Google' hotwording is disabled by default in open source builds. Set to
+  # true to enable. (This will download a closed-source NaCl module at startup.)
+  # Chrome-branded builds have this enabled by default.
+  enable_hotwording = is_chrome_branded && is_chromeos
+
   # Enables proprietary codecs and demuxers; e.g. H264, MOV, AAC, and MP3.
   # Android OS includes support for proprietary codecs regardless of building
   # Chromium or Google Chrome. We also ship Google Chrome and Chromecast with
   # proprietary codecs.
   proprietary_codecs = is_android || is_chrome_branded || is_chromecast
 
   enable_configuration_policy = !is_ios
 
   # Enables support for background apps.
   enable_background = !is_ios && !is_android
@@ skipping 124 matching lines @@
 
 # Option controlling the use of GConf (the classic GNOME configuration
 # system).
 use_gconf = is_linux && !is_chromeos && !is_chromecast && !is_headless
 
 # Enable WebVR support by default on Android
 # Still requires command line flag to access API
 enable_webvr = is_android
 
 use_gio = is_desktop_linux && !is_headless