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This moves the presentation web tests into wpt_internal and adapts them
to use the newer Mojo JS modules. Since this already produces quite a
bit of churn in the tests, the tests here are also opportunistically
modernized where feasible, particularly concerning asynchronous logic.

Bug: 1004256
Change-Id: I5515325cfc808cd5f0e7dff51840a94c4078b4b7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2634278
Commit-Queue: Ken Rockot <rockot@google.com>
Reviewed-by: mark a. foltz <mfoltz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846373}