[BMO] Chrome://apps uninstall dialog now tied to browser window

I accidentally didn't associate the uninstall window to the browser
window when updating the uninstall code to support BMO.

R=calamity@chromium.org, loyso@chromium.org

Fixed: 1070159
Change-Id: I2fa4e50bd28af7283b57491d0e49c3a60350566a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2147545
Auto-Submit: Daniel Murphy <dmurph@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Reviewed-by: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#758742}

chrome/browser/ui/webui/ntp/app_launcher_handler.cc

@@ -876,13 +876,14 @@ void AppLauncherHandler::HandleUninstallApp(const base::ListValue* args) {
       web_app_provider_->install_finalizer().UninstallExternalAppByUser(
           extension_id_prompting_, std::move(uninstall_success_callback));
     } else {
+      Browser* browser =
+          chrome::FindBrowserWithWebContents(web_ui()->GetWebContents());
       web_app::WebAppUiManagerImpl::Get(Profile::FromWebUI(web_ui()))
           ->dialog_manager()
           .UninstallWebApp(
               extension_id_prompting_,
               web_app::WebAppDialogManager::UninstallSource::kAppsPage,
-              /*browser_window=*/nullptr,
-              std::move(uninstall_success_callback));
+              browser->window(), std::move(uninstall_success_callback));
     }
     return;
   }