While investigating crbug 854711, I noticed now might be a good time to at least deduplicate:
[WPT]: external/wpt/media-source/mediasource-append-buffer.html, and
[BLINK]: http/tests/media/media-source/mediasource-append-buffer.html

On inspection, it looks like WPT has some general improvements to many of the common cases (like listening for and failing on 'error' event), BLINK has some bulk " -> ' changes, but there are some tests currently only in just one of each of WPT/BLINK:

WPT has, BLINK doesn't have:
* "Test appendBuffer events order."
* "Test slow appending does not trigger stalled events."

BLINK has, WPT doesn't have:
* "Test abort in the middle of a media segment."
* Conditional (if window.SharedArrayBuffer) "Test appending SharedArrayBuffer view."

This bug tracks merging the full mediasource-append-buffer.html test functionality into the external/wpt version, and if there are any cases required only in Chrome, to put those in a *-chrome version of the test in BLINK's folder.