[Chromoting] Add enable_remoting_jscompile GN arg.

This change allows you to use "gn args" to set enable_remoting_jscompile
to true to have it enabled all the time in GN builds.

BUG=

Review URL: https://codereview.chromium.org/1183533005

Cr-Commit-Position: refs/heads/master@{#334279}
diff --git a/remoting/remoting_options.gni b/remoting/remoting_options.gni
index 771a185..df1292f 100644
--- a/remoting/remoting_options.gni
+++ b/remoting/remoting_options.gni
@@ -2,8 +2,11 @@
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
-# Set this to run the jscompile checks after building the webapp.
-run_jscompile = false
+# These arguments can be overridden from the command line (see "gn help args").
+declare_args() {
+  # Set this to run the jscompile checks after building the webapp.
+  enable_remoting_jscompile = false
+}
 
 # Set this to enable cast mode on the android client.
 enable_cast = 0