Intent to Migrate (WICG → WebPerf WG): Paint Timing API & Device Memory

As discussed on the last WG call [1], we are migrating following specs from
WICG to WebPerf WG:

*# Paint Timing API*
Spec: https://github.com/WICG/paint-timing
<https://github.com/wicg/paint-timing>
Editor: panicker@chromium.org

This specification defines an API that can be used to capture a series of
key moments (First Paint, First Contentful Paint) during pageload which
developers care about.


*# Device Memory*
Spec: *https://github.com/WICG/device-memory
<https://github.com/WICG/device-memory>*
Editors: panicker@chromium.org

This specification defines a new HTTP Client Hints header and a web exposed
API to surface device capability for memory (RAM). The JS API will be a
convenience for analytics reporting and may be used to make runtime
decisions eg. using more storage vs. making additional requests, requesting
appropriate resources from the server etc.


[1] https://lists.w3.org/Archives/Public/public-web-perf/2017Aug/0005.html