[bazel] Show CanvasKit can be loaded in POC karma_test

In order to load CanvasKit, we need to add support for statically
served files. On the karma side, this is done by adding an
object [1] to the files list (example: [2]).

Then, we need to include canvaskit.js in with the karma test
files and use the callback to load canvaskit.wasm from the
correct file location.

[1] http://karma-runner.github.io/6.3/config/files.html
[2] https://github.com/google/skia/blob/4f7b6560123d89cac2a9ec6eb71a54b5bc2fe56c/modules/canvaskit/karma.conf.js#L13
Change-Id: I7482d6e949a5e8efd0ca882efe5afbe0dc16c0e4
Bug: skia:12541
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/510736
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
5 files changed