Used to be:

Failure: expected <foo> is not an instance of <Bar> but of < Baz>> found <undefined>

Should be:

Failure: <foo> is not an instance of <Bar> but of <Baz>

BUG=

Review-Url: https://codereview.chromium.org/2413153004
Cr-Commit-Position: refs/heads/master@{#40319}