Show request and pending dialog for theme

There is no request dialog and request pending dialog for theme request.
And the request is confirmed automatically.

Enable these dialogs for theme request for better consistency as admin
is able to block theme like an extension

Bug: 1077349

Change-Id: I96fe2bafc59f97851d089c646294b33098f18492
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2175740Reviewed-by: Karan Bhatia <karandeepb@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#802904}

chrome/browser/extensions/extension_install_prompt.cc

@@ -550,7 +550,9 @@ void ExtensionInstallPrompt::ShowDialog(
   // We special-case themes to not show any confirm UI. Instead they are
   // immediately installed, and then we show an infobar (see OnInstallSuccess)
   // to allow the user to revert if they don't like it.
-  if (extension->is_theme() && extension->from_webstore()) {
+  if (extension->is_theme() && extension->from_webstore() &&
+      prompt_->type() != EXTENSION_REQUEST_PROMPT &&
+      prompt_->type() != EXTENSION_PENDING_REQUEST_PROMPT) {
     std::move(done_callback_).Run(Result::ACCEPTED);
     return;
   }