With this change, Vulkan-ValidationLayers will allow the specified
extensions to pass through, instead of being nulled out:

* VK_STRUCTURE_TYPE_SAMPLER_FILTERING_PRECISION_GOOGLE
* VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_PROVOKING_VERTEX_FEATURES_EXT

Bug: b/159027603
Bug: b/154620295
Change-Id: I0ace3acdac06a6c115834ef88b0c883fa2dd4744
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2246304
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>