Fix the wrong app opened issue.

ChromeNewWindowClient::OpenFileManager should open the file app, based
on the previous code before the CL:2121518 is landed. This CL fix the
issue caused by CL:2121518.

TBR=xiyuan@chromium.org

BUG=1067447

Change-Id: Icfd83c629760ff0913cf18801540c5374370efb9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2133991
Commit-Queue: Nancy Wang <nancylingwang@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#756127}

chrome/browser/ui/ash/chrome_new_window_client.cc

@@ -306,8 +306,7 @@ void ChromeNewWindowClient::OpenFileManager() {
       apps::AppServiceProxyFactory::GetForProfile(profile);
   DCHECK(proxy);
   proxy->AppRegistryCache().ForOneApp(
-      extension_misc::kWallpaperManagerId,
-      [proxy](const apps::AppUpdate& update) {
+      file_manager::kFileManagerAppId, [proxy](const apps::AppUpdate& update) {
         if (update.Readiness() == apps::mojom::Readiness::kReady) {
           proxy->Launch(update.AppId(),
                         apps::GetEventFlags(