This way gr-diff can be reused with a different server.
I decided to move tests concerning the server calls almost unchanged to
gr-diff-host, even when they reach into gr-diff and deeper to check if
certain things happened as a result of loading.
I added similar tests, minus the actual loading, back to gr-diff. This
results in a bit of duplicated test logic, because e.g. the rendering
is tested both in gr-diff and gr-diff-host. I think that is worth it to
reduce the likelihood I broke something.
Bug: Issue 9623
Change-Id: Ib460094eb8d5b8e856c0d7954ee801fa3b5946d3
b1a7967be2