[Extensions] Update background application list model test to use manifest v2

Update background_application_list_model_unittest.cc to generate
extensions with manifest_version 2.

Bug: 816679
Change-Id: Icb245afea008fb2bdf57ae20e7289539aa39724e
Reviewed-on: https://chromium-review.googlesource.com/1008605
Commit-Queue: Drew Wilson <atwilson@chromium.org>
Reviewed-by: Drew Wilson <atwilson@chromium.org>
Cr-Commit-Position: refs/heads/master@{#550142}

chrome/browser/background/background_application_list_model_unittest.cc

@@ -88,6 +88,7 @@ static scoped_refptr<Extension> CreateExtension(
     bool background_permission) {
   base::DictionaryValue manifest;
   manifest.SetString(extensions::manifest_keys::kVersion, "1.0.0.0");
+  manifest.SetInteger(extensions::manifest_keys::kManifestVersion, 2);
   manifest.SetString(extensions::manifest_keys::kName, name);
   auto permissions = std::make_unique<base::ListValue>();
   if (background_permission) {