This cl changes the software backend used for
running viz_unittests and cc_unittests from
SwiftShader GL to SwANGLE (ANGLE on SwiftShader
Vulkan). Other tests suites may be affected.

From this cl, performance expectations for test
runs will likely change. For example, cc_unittests
appears to run faster, while viz_unittests and
views_unittests appear to run slower. Note that
this is still using the validating command decoder,
and once the OOP Raster tests can run on the
passthrough command decoder, we'll be able to use
it and gain some performance on all these test runs.

Bug: chromium:1060139
Change-Id: Ia243f05f3e9f54dc6f6dfaa3041021fc28818b2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2532042
Commit-Queue: Alexis Hétu <sugoi@chromium.org>
Reviewed-by: weiliangc <weiliangc@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Cr-Commit-Position: refs/heads/master@{#834246}