Refactor Signal utils into template classes. This will allow us to pass on extra information to the receiving end, such as the specific texture levels that are dirty. BUG=angleproject:1635 Change-Id: Idb7ca1d625499e50e7712c458b694f6e9bfc0595 Reviewed-on: https://chromium-review.googlesource.com/453382 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Geoff Lang <geofflang@chromium.org>