GitLab

 - Add a new |polymer3_args| collection of JS Compiler flags in
   closure_args.gni, needed for type-checking Polymer3 modules.
 - Adding a new |is_polymer3| parameter to js_binary/js_type_check
   (defaults to false)
 - Updating compile_js.gni to not use polymer_externs for Polymer3,
   since Polymer itself is passed to the compiler (otherwise compilation
   fails)
 - Add js_type_check() targets for cr-button, cr-checkbox, cr-toast,
   cr-toggle, cr-view-manager.

Also fixing a bug where editing closure_args.gni did not trigger
js_type_check() targets to re-run.

Bug: 970885
Change-Id: I9b43eac504f80fd43e542565fc9746579a4ba10a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726873
Commit-Queue: Demetrios Papadopoulos <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683808}