Chrome is showing rendering issues on Linux/Nvidia after returning from
the lock screen. This could be related to the fact that Nvidia drivers
are not able to guarantee conformance after certain events.
By exposing this extension, we can instruct Chrome to reinitialize
contexts after they are purged by the driver. If this is not explicitly
requested, we can still generate an UnknownContextReset to tell apps
to discard the invalid context anyway.

Bug: chromium:1113040
Change-Id: Ie99b6356cc27fea33643d61b1d74f4f68a271d70
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2453689Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>