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
(cherry picked from commit 96a49a48)
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2491114Reviewed-by: Kenneth Russell <kbr@chromium.org>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>