[fuchsia] Exclude WebUI static resources on release builds.

Adds a new GN arg "include_webui_resources", which if set, includes
the WebUI resources needed for rendering chrome://gpu.

The flag is unset on release builds by default, to reduce
the footprint of official WebEngine prebuilts.

Bug: 1082420
Change-Id: Id91a4e124b976cff01ef0b974b378d3a12235a84
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2199411
Auto-Submit: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#768569}

fuchsia/engine/BUILD.gn

@@ -15,6 +15,17 @@ config("web_engine_implementation") {
   defines = [ "WEB_ENGINE_IMPLEMENTATION" ]
 }
 
+declare_args() {
+  # If set, includes assets served under chrome://resources in web_engine.pak.
+  # They are required by some test-oriented diagnostic views like
+  # chrome://gpu.
+  # Including the resources will increase the application size, so this value
+  # should be left unset for release builds.
+  # TODO(crbug.com/1082420): change default to 'false' once all bots that run
+  # GPU integration tests set this flag to 'true'.
+  include_webui_resources = !is_official_build
+}
+
 mojom("mojom") {
   sources = [
     "on_load_script_injector.mojom",
@@ -41,11 +52,14 @@ 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",
   ]
 
+  if (include_webui_resources) {
+    sources += [ "$root_gen_dir/ui/resources/webui_resources.pak" ]
+  }
+
   deps = [
     "//components/resources:components_resources",
     "//components/strings",