Fix cases where RunLoop is created without a MessageLoop.

The tests in these cases can pass only if Quit is called before Run, or
if Run is never called at all. If this is guaranteed to hold true, then
RunLoop is not needed (such as in timer_unittest.cc). Other cases (where
it is not guaranteed) are tests that can crash occasionally.

BUG=668707

Review-Url: https://codereview.chromium.org/2571473002
Cr-Commit-Position: refs/heads/master@{#438126}
9 files changed