Validate origins when generating subdomain tokens

Subdomain tokens will match against any subdomains of the given origin.
This relaxed matching should not be applied when subdomains represent
separate logical sites (e.g. <user>.github.io). Thus, subdomain tokens
are not to be issued for such domains. For more detail, see the last
question in the Origin Trials developer guide:
https://github.com/jpchase/OriginTrials/blob/gh-pages/developer-guide.md

This CL adds a utility to validate that a origin is not found in the
Public Suffix List. The token generation script will now call the
utility to check the origin, only for subdomain tokens. The utility
is used when the generation script is manually run by the origin
trials team to issue tokens. The intent is to automate the origin
checks, to reduce the number of manual steps in issuing tokens.

BUG=658856

Review-Url: https://codereview.chromium.org/2456053004
Cr-Original-Commit-Position: refs/heads/master@{#440554}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6205808cb4e9c61264e4aa48676e2f5833a61326

config/linux/gconf/BUILD.gn

@@ -8,11 +8,6 @@ import("//build/config/linux/pkg_config.gni")
 # CrOS doesn't install GTK, gconf or any gnome packages.
 assert(!is_chromeos && use_gconf)
 
-# These packages should _only_ be expected when building for a target.
-# If these extra checks are not run, gconf is required when building host
-# tools for a CrOS build.
-assert(current_toolchain == default_toolchain)
-
 pkg_config("gconf") {
   packages = [ "gconf-2.0" ]
   defines = [ "USE_GCONF" ]