Extensions WebUI: Add missing images to auto-generated grd file.

These were missed at r814094.

Bug: 1132403
Change-Id: Id504b4e2b39fd8c232bc992d31ed9f5b75981ec3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2461206Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: dpapad <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815192}

chrome/browser/resources/extensions/BUILD.gn

@@ -47,7 +47,6 @@ preprocess_grit("preprocess") {
   out_folder = "$target_gen_dir/$preprocess_folder"
   out_manifest = "$target_gen_dir/$preprocess_manifest"
   in_files = [
-    "extensions.html",
     "drag_and_drop_handler.js",
     "extensions.js",
     "item_behavior.js",
@@ -56,6 +55,12 @@ preprocess_grit("preprocess") {
     "navigation_helper.js",
     "service.js",
     "shortcut_util.js",
+
+    # TODO(dpapad): Pass these directly to the generate_grd() target above, once
+    # support for that is added, as part of crbug.com/1132403.
+    "extensions.html",
+    "checkup_image_dark.svg",
+    "checkup_image.svg",
   ]
 
   if (is_chromeos) {