WebApp: Fix for proper removal of the web app icon on web app uninstalled.

Observe OnWebAppWillBeUninstalled instead of OnWebAppUninstalled.

It's too late to obtain the app pointer from the registrar after a web app
uninstall (deletion) happened.

Bug: 1029221
Change-Id: I7794ed4fa7ed52ac396949eed88bd4514ed2154a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1975473Reviewed-by: Nancy Wang <nancylingwang@chromium.org>
Commit-Queue: Alexey Baskakov <loyso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726599}

chrome/browser/apps/app_service/web_apps.cc

@@ -404,7 +404,7 @@ void WebApps::OnWebAppInstalled(const web_app::AppId& app_id) {
   }
 }
 
-void WebApps::OnWebAppUninstalled(const web_app::AppId& app_id) {
+void WebApps::OnWebAppWillBeUninstalled(const web_app::AppId& app_id) {
   const web_app::WebApp* web_app = GetWebApp(app_id);
   if (!web_app) {
     return;

chrome/browser/apps/app_service/web_apps.h

@@ -96,7 +96,7 @@ class WebApps : public apps::mojom::Publisher,
 
   // web_app::AppRegistrarObserver:
   void OnWebAppInstalled(const web_app::AppId& app_id) override;
-  void OnWebAppUninstalled(const web_app::AppId& app_id) override;
+  void OnWebAppWillBeUninstalled(const web_app::AppId& app_id) override;
   void OnAppRegistrarDestroyed() override;
   // TODO(loyso): Implement app->last_launch_time field for the new system.