Make RCSignalObserver use the new Node observer interfaces

Change-Id: Ia06db6865d75c1712e2de27838d36087628b2bdf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1688529
Commit-Queue: Chris Hamilton <chrisha@chromium.org>
Reviewed-by: Chris Hamilton <chrisha@chromium.org>
Cr-Commit-Position: refs/heads/master@{#675024}
6 files changed