Build NaCl in the CrOS GN builds and make sure "all" works

Fixing "all" involved a tweak to remoting to not try to
build remote_assistance_host (which shouldn't be built
on CrOS and isn't in GYP).

R=petermayo@chromium.org, mcgrathr@chromium.org, sergeyu@chromium.org, bbudge@chromium.org, bbudge@chromium.org
BUG=433082

Review URL: https://codereview.chromium.org/1417823006

Cr-Original-Commit-Position: refs/heads/master@{#359921}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: f1e91ca130c57fbabb2f990e640a6d0bc09214c2

config/features.gni

@@ -39,8 +39,8 @@ declare_args() {
   # the commented out logic.
   # Eventually we want this to be:
   #   enable_nacl = !is_ios && !is_android && !is_chromecast
-  enable_nacl = (is_mac || (is_linux && !is_chromeos) || is_nacl) &&
-                current_cpu != "mipsel" && !is_chromecast
+  enable_nacl = (is_linux || is_mac || is_nacl) && current_cpu != "mipsel" &&
+                !is_chromecast
   enable_nacl_untrusted = enable_nacl
   enable_pnacl = enable_nacl_untrusted