Upstream service wrkr "respond with" tests to WPT

**(fetch-event-)respond-with-readable-stream**

**(fetch-event-)respond-with-response-body-with-invalid-chunk**

Re-locate test files to Web Platform Test directory for eventual
automated upstreaming. Modify file names according to convention set by
related tests in that project. Update resource URLs to suitable values
for that project. Schedule frame removal to occur following test
completion. Introduce a "use strict" directive. Simplify Promise
creation.

BUG=688116
R=falken@chromium.org

Review-Url: https://codereview.chromium.org/2893793004
Cr-Commit-Position: refs/heads/master@{#473232}
6 files changed