Import web-platform-tests@5a8700479d98852455bee6117558897867eb278a

Using update-w3c-deps in Blink 7bebfa461eab56d6e2f78d8c42a2130ab538c305.

After the import, some paths in TestExpectations needed to be updated
(due to structural changes in web-platform-tests/mediacapture-streams),
plus there are some new and updated expected failures and timeouts.

BUG=600261

Review URL: https://codereview.chromium.org/1854003004

Cr-Commit-Position: refs/heads/master@{#385996}
278 files changed