Fix a shutdown crash when BMO is enabled on Chrome OS.

When web apps are uninstalled and the clear site data option is
selected, the |web_app| object was being accessed after uninstallation
was completed, causing a DCHECK failure. This CL rearranges the call to
clear site data so that its origin is computed before uninstallation.

BUG=1084394

Change-Id: Iab3705096f5658cc30e2aa08c43d56247281cf5d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2208156Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#770009}

chrome/browser/apps/app_service/web_apps_chromeos.cc

@@ -134,8 +134,10 @@ void WebAppsChromeOs::Uninstall(const std::string& app_id,
   DCHECK(provider());
   DCHECK(provider()->install_finalizer().CanUserUninstallExternalApp(app_id));
 
+  auto origin = url::Origin::Create(web_app->launch_url());
   provider()->install_finalizer().UninstallExternalAppByUser(app_id,
                                                              base::DoNothing());
+  web_app = nullptr;
 
   if (!clear_site_data) {
     // TODO(loyso): Add UMA_HISTOGRAM_ENUMERATION here.
@@ -152,8 +154,7 @@ void WebAppsChromeOs::Uninstall(const std::string& app_id,
                                return browser_context;
                              },
                              base::Unretained(profile())),
-                         url::Origin::Create(web_app->launch_url()),
-                         kClearCookies, kClearStorage, kClearCache,
+                         origin, kClearCookies, kClearStorage, kClearCache,
                          kAvoidClosingConnections, base::DoNothing());
 }