Fail tests fast if overriding the Windows registry fails.

All calls to RegistryOverrideManager::OverrideRegistry are now wrapped
in ASSERT_NO_FATAL_FAILURE, as are a few helper functions in
RegistryOverrideManagerTest that should have been.

BUG=688878
TBR=brettw@chromium.org

Review-Url: https://codereview.chromium.org/2692843002
Cr-Commit-Position: refs/heads/master@{#450288}
42 files changed