[ngatoy] Make an explicit ID class and simplify Cmd class

Bug: skia:11837
Change-Id: I44b8f02555c1ed7e2f1bf0872bf41f78d1eb5d25
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/417003
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Robert Phillips <robertphillips@google.com>
7 files changed