Automated test case for 487928.

Reproducing this bug requires the embedder to fire timers, something the
single-pass pdfium-test binary doesn't do properly at the present. So
we modify the embedder test delegate to allow the immediate triggering
of the same.

Perform some cleanup along the way by removing EmbedderTestDefaultDelegate
-- it buys us nothing over the the no-op one.

And, of course, v8 initialization is busted again, and we need v8 here.

R=thestig@chromium.org

Review URL: https://codereview.chromium.org/1153213004
9 files changed