Vulkan returns timestamps in cycles, which needs to be converted to
nanoseconds (by multiplying by limits.timestampPeriod) for GLES.

On NVidia, this multiplier seems to be 1 for a majority of their
hardware, while the timer has less and more varying granularity on AMD,
Intel and others.

Bug: angleproject:2885
Change-Id: I34e08ad386e06619170975039385ce35cab025a5
Reviewed-on: https://chromium-review.googlesource.com/c/1436835Reviewed-by: Jamie Madill <jmadill@chromium.org>
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>