[Chromecast] Rename disable_display flag to is_cast_audio_only.

build/config/chromecast_build.gni

 # 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.
 
 # The args declared in this file should be referenced by components outside of
 # //chromecast. Args needed only in //chromecast should be declared in
 # //chromecast/chromecast.gni.
 declare_args() {
   # Set this true for a Chromecast build. Chromecast builds are supported on
   # Linux and Android.
   is_chromecast = false
 
   # Set this true for an audio-only Chromecast build.
-  disable_display = false
+  is_cast_audio_only = false
 }
 
 # Note(slan): This arg depends on the value of is_chromecast, and thus must be
 # declared in a separate block. These blocks can be combined when/if
 # crbug.com/542846 is resolved.
 declare_args() {
   # True if Chromecast build is targeted for linux desktop. This type of build
   # is useful for testing and development, but currently supports only a subset
   # of Cast functionality. Though this defaults to true for x86 Linux devices,
   # this should be overriden manually for an embedded x86 build.
   # TODO(slan): Remove instances of this when x86 is a fully supported platform.
   is_cast_desktop_build = is_chromecast && target_os == "linux" &&
                           (target_cpu == "x86" || target_cpu == "x64")
 }
 
 # Assert that Chromecast is being built for a supported platform.
 assert(is_linux || is_android || !is_chromecast,
        "Chromecast builds are not supported on $target_os")
 
-# Assert that disable_display and is_cast_desktop_build are both false on a
+# Assert that is_cast_audio_only and is_cast_desktop_build are both false on a
 # non-Chromecast build.
-assert(is_chromecast || !(disable_display || is_cast_desktop_build))
+assert(is_chromecast || (!is_cast_audio_only && !is_cast_desktop_build))