Previously it was enabled by default in every build that includes
D3D11. This would impact CPU overhead in Chrome and other targets
that don't need this feature.

Bug: angleproject:5828
Change-Id: Ic9d700847c72978540b66fdaf7a62f959779f2e6
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2809855Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Doug Horn <doughorn@google.com>
Commit-Queue: Jamie Madill <jmadill@chromium.org>