Mark js_modules as not needed if JS is not compiled

js_modules is used by closure during compilation.
It is not needed if there is no compilation.

This CL fixes the gn error on js_modules not being used
when compiling with compile_javascript=false.

Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I9de8b97214e97c068f55b770a4f296bb1c9bee4d
Reviewed-on: https://chromium-review.googlesource.com/1024839
Commit-Queue: Olivier Robin <olivierrobin@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553283}

ios/web/js_compile.gni

@@ -196,6 +196,7 @@ template("js_compile_checked") {
     }
   } else {
     bundle_data(target_name) {
+      not_needed(invoker, [ "js_modules" ])
       forward_variables_from(invoker,
                              [
                                "data_deps",