[Fuchsia] Add WebUI common resources to WebEngine resource PAK.

Adds some JS resources served under chrome://resources/, which are
included by other WebUI pages like chrome://gpu.

Bug: 1017316
Change-Id: Iaa76bc6d561dea2fef63d4145e8224c35ae9b30c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1976592Reviewed-by: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726635}

fuchsia/engine/BUILD.gn

@@ -39,6 +39,7 @@ repack("web_engine_pak") {
     "$root_gen_dir/third_party/blink/public/resources/blink_scaled_resources_100_percent.pak",
     "$root_gen_dir/third_party/blink/public/strings/blink_strings_en-US.pak",
     "$root_gen_dir/ui/resources/ui_resources_100_percent.pak",
+    "$root_gen_dir/ui/resources/webui_resources.pak",
     "$root_gen_dir/ui/strings/app_locale_settings_en-US.pak",
     "$root_gen_dir/ui/strings/ui_strings_en-US.pak",
   ]