Make asynchronous test configuration explicit

For asynchronous tests, the contract between test file and test runner
is implicit: runners are expected to inspect the source code for
references to a global `$DONE` identifier.

Promote a more explicit contract between test file and test runner by
introducing a new frontmatter "tag", `async`. This brings asynchronous
test configuration in-line with other configuration mechanisms and also
provides a more natural means of test filtering.

The modifications to test files was made programatically using the
`grep` and `sed` utilities:

    $ grep "\$DONE" test/ -r --files-with-match --null | \
        xargs -0 sed -i 's/^\(flags:\s*\)\[/\1[async, /g'
    $ grep "\$DONE" test/ -rl --null | \
        xargs -0 grep -E '^flags:' --files-without-match --null | \
        xargs -0 sed -i 's/^---\*\//flags: [async]\n---*\//'

1 files changed, 1 insertions, 0 deletions

diff --git a/test/built-ins/Promise/race/resolve-self.js b/test/built-ins/Promise/race/resolve-self.js
index 511a03200..9bf40fc47 100644
--- a/test/built-ins/Promise/race/resolve-self.js
+++ b/test/built-ins/Promise/race/resolve-self.js
@@ -20,6 +20,7 @@ info: >
     6. If SameValue(resolution, promise) is true, then
        a. Let selfResolutionError be a newly created TypeError object.
        b. Return RejectPromise(promise, selfResolutionError).
+flags: [async]
 ---*/
 
 var self, resolve;