Add enable_vr_shell build time flag and show icon in Daydream app luncher

chrome/common/features.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.
 
 # This is the GN version of //chrome/chrome_features.gypi.
 # Please keep in sync!
 
 import("//build/config/chromecast_build.gni")
 
 declare_args() {
@@ skipping 13 matching lines @@
 
   # Enables support for background apps.
   enable_background = !is_ios && !is_android && !is_chromecast
 
   enable_one_click_signin =
       is_win || is_mac || (is_linux && !is_chromeos && !is_chromecast)
 
   # Set to true to bundle all the mash related mojo services into chrome.
   # Specify --mash to chrome to have chrome start the mash environment.
   enable_package_mash_services = is_chromeos
+
+  # Enables vr shell.
+  enable_vr_shell = false && is_android

[Ted C, 2016/08/02 21:38:11]

umm...while my gn foo is quite weak, this looks particularly odd to me.  why
isn't it just false?

[bshe, 2016/08/02 22:26:59]

Good question. I was trying to restrice other platforms use this build flag as
we only support Android initially. And I think I can mix default value with
value of "is_android". "gn args --list out/Debug | grep vr_shell" shows that the
default value is "false" without "is_android" included. So I imagine when
processing it, false is replaced with the value we set in gn args first and then
evaluated here. But I am not 100% sure
Anyway, I agree this is not very readable and we dont use it outside of Android
anyway. So remove "is_android" here. 

 }
 
 chrome_grit_defines = [
   "enable_background=$enable_background",
   "enable_google_now=$enable_google_now",
   "use_vulcanize=$use_vulcanize",
 ]