Add docker-based infrastructure for Gold/lottie-web integration

This adds 2 docker containers (based on the ones used for PathKit
added in https://skia-review.googlesource.com/c/skia/+/147042)
which bundle Chrome and puppeteer to allow the lottiecap.js
to be run anywhere.

This adds a recipe (test_lottie_web.py) to drive the docker
container and do a little bit of set-up (and a few docs/bug
fixes discovered in the test_pathkit.py that it was based on).

Additionally, this modifies lottiecap.js to support POSTing
output to a running go server (again, the same as PathKit)
which has the image data hashed and the metadata added to
a large JSON output.

This re-works driver.html to avoid re-loading the JSON object
25 times. The performance boost is important because, right now,
the lottie files are processed individually.

In a future CL, I want to address the two TODOs in
lottie-web-aggregator.go

Bug: skia:8108
Change-Id: I100c9ce23dcc5033a27287211cbf0db898960da9
Reviewed-on: https://skia-review.googlesource.com/149282
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Reviewed-by: Joe Gregorio <jcgregorio@google.com>
Reviewed-by: Stephan Altmueller <stephana@google.com>
22 files changed