This reduces the test time to run in several ms instead of almost
seconds per iteration. It allows us to use the perf test runner harness
to check test performance more accurately by increasing the sample
count.

It first reduces the test iteration count to reduce total test time.
It also refactors the test contents to not allocate new objects and
memory with every test iteration. This gives a better sampling of what
the test is obsering: texture upload performance.

Also allows tests that like to track GPU time to be used with the NULL
device option.

Bug: angleproject:3712
Change-Id: Idacc3e3b424f8882d7680769b27d1f04146ea65d
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1707112Reviewed-by: Tobin Ehlis <tobine@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>