Re-enable closure compiler checks for test mojom

The js_type_check for some WebUI test mojom was inadvertently broken to
no longer perform most of the useful type checks. This fixes that.

Bug: 1004256
Change-Id: Ic8e9d4bdc098daa84c591a72f9c82e53b9e7d87f
Tbr: dpapad@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2517486Reviewed-by: Ken Rockot <rockot@google.com>
Commit-Queue: Ken Rockot <rockot@google.com>
Cr-Commit-Position: refs/heads/master@{#824191}

content/test/BUILD.gn

@@ -808,7 +808,7 @@ js_library("web_ui_mojo_test_js") {
 js_type_check("web_ui_mojo_test_js_type_check") {
   uses_js_modules = true
   deps = [ ":web_ui_mojo_test_js" ]
-  closure_flags = mojom_js_args
+  closure_flags = default_closure_args + mojom_js_args
 }
 
 mojom("mojo_web_test_bindings") {