Ensure tests have an active task runner

Ensure tests have an active task runner

This patch modifies all tests to have a more realistic threading set-up by either:

  a) adding a TestBrowserThreadBundle
  b) constructing any existing TestBrowserThreadBundle earlier or
  c) adding a MessageLoop as appropriate.

This makes it possible to later migrate base/ from MessageLoopProxy over to
ThreadTaskRunnerHandle, which requires an active task runner on the current thread.

BUG=465354

Review URL: https://codereview.chromium.org/1086733002

Cr-Commit-Position: refs/heads/master@{#327067}