This CL adds a fence wait when we get more than 100 serials behind the
device. This fixes an ASSERT when unit tests or offscreen performance
tests get way ahead of the device.

Bug: angleproject:3630
Bug: angleproject:4281
Change-Id: I90f9af1b2ceb2b1cd9f2f638d6d84caaeeb83bb1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2057351
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Ian Elliott <ianelliott@google.com>
Reviewed-by: Tim Van Patten <timvp@google.com>