RELAND: MediaStreamManager: listen to and log OnThermalStateChange

Original CL got reverted bc it broke ASAN Mac Gpu FYI bots
https://crbug.com/1087096

Cq-Include-Trybots=luci.chromium.try:gpu-fyi-try-mac-asan

TBR=guidou@chromium.org for media_stream_manager that is unmodified.

Original CL description ------------------------------------------------
crrev.com/c/2195334 just landed PowerObserver::OnThermalStateChange,
this CL listens to it from MediaStreamManager and logs it in the
WebRTC log.

The utility function PowerMonitorSource::DeviceThermalStateToString
gets #if DCHECK_IS_ON() removed to be used from the new code, which
runs also in non-dcheck_always_on builds.

Bug: 1071431
Change-Id: I5ea476c48c5d4c2de0be9b36b4030b81684cca75
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2207410
Reviewed-by: François Doray <fdoray@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#771045}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2229471
Reviewed-by: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#775899}