WebAssembly's specification tests use a timeout annotation.
This change allows the shared testrunner to use it to calculate
the testcase timeout.

Currently, the allowed timeout values are: long. Other values will
emit a warning.

Change-Id: Id7f453f5fd49854c8f53ff86ef2ec58aa0ae8748
Reviewed-on: https://chromium-review.googlesource.com/c/1480376Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Sven Sauleau <ssauleau@igalia.com>
Cr-Commit-Position: refs/heads/master@{#59919}