[canvaskit] Add task driver for running GMs on WASM/WebGL.

This loads in the known digests from Gold, starts the test
harness (which runs the GMs using puppeteer) and then uses
goldctl to upload the results to Gold when finished.

This will fail (and should not be landed) until
https://skia-review.googlesource.com/c/buildbot/+/328156
makes it into goldctl and the cipd build.

Bug: skia:10812
Change-Id: I89e5cf188d8f2adeba4ff676525d9bfbdcb46d5a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/328380
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
7 files changed