Fix installing Chrome apps in offline Demo Mode

Use EXTERNAL_POLICY[_DOWNLOAD] for the manifest locations
so Chrome apps are allowed to install.

Bug: 925419
Change-Id: Ie65c76a28d8ebe5c63ee4d54cd2449b8759f9e18
Reviewed-on: https://chromium-review.googlesource.com/c/1437543
Auto-Submit: Michael Giuffrida <michaelpg@chromium.org>
Commit-Queue: Ben Wells <benwells@chromium.org>
Reviewed-by: Ben Wells <benwells@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#626932}(cherry picked from commit 00afa042e71d6209e13d3c32041aaed9fb8173b8)
Reviewed-on: https://chromium-review.googlesource.com/c/1453062
Cr-Commit-Position: refs/branch-heads/3683@{#189}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
diff --git a/chrome/browser/extensions/external_provider_impl.cc b/chrome/browser/extensions/external_provider_impl.cc
index d9ced93..96c0e4d 100644
--- a/chrome/browser/extensions/external_provider_impl.cc
+++ b/chrome/browser/extensions/external_provider_impl.cc
@@ -740,8 +740,8 @@
         base::MakeRefCounted<chromeos::DemoExtensionsExternalLoader>(cache_dir);
     std::unique_ptr<ExternalProviderImpl> demo_apps_provider =
         std::make_unique<ExternalProviderImpl>(
-            service, loader, profile, Manifest::EXTERNAL_PREF,
-            Manifest::EXTERNAL_PREF_DOWNLOAD, Extension::NO_FLAGS);
+            service, loader, profile, Manifest::EXTERNAL_POLICY,
+            Manifest::EXTERNAL_POLICY_DOWNLOAD, Extension::NO_FLAGS);
     demo_apps_provider->set_auto_acknowledge(true);
     demo_apps_provider->set_install_immediately(true);
     chromeos::DemoSession::Get()->SetExtensionsExternalLoader(loader);