Make editing/undo/undo-after-event-edited.html stable

This patch changes a test script, undo-after-event-edited.html, stable, by executing JavaScript after document finished loading.

When calling Range.extractContents() for selection selected whole document w/o body, SimplifiedBackwardsTextIterator creates Range object with DocumentType which is illegal argument for Range construction.

BUG=242444
R=ojan@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=151633

[yosin_UTC9, 2013-05-27 10:04:21]

Could you review this patch?
Thanks in advance.

[ojan, 2013-05-31 20:49:50]

I think SimplifiedBackwardsTextIterator should be fixed to not trying to create
a Range with a DocumentType node. Then this test would not be flaky anymore and
we'd fix an actual bug in the C++ side, right?

[yosin_UTC9, 2013-06-03 01:37:59]

On 2013/05/31 20:49:50, ojan wrote:
> I think SimplifiedBackwardsTextIterator should be fixed to not trying to
create
> a Range with a DocumentType node. Then this test would not be flaky anymore
and
> we'd fix an actual bug in the C++ side, right?

No. The test works different content, one is whole html, as expected, another is
before body, or head only.
setTimeout() is a source of flaky.

Not creating a Range with DocumentType node is yet another issue.

[ojan, 2013-06-03 07:17:32]

lgtm

Got it. Makes sense.

[yosin_UTC9, 2013-06-03 07:56:01]

Committed patchset #2 manually as r151633 (presubmit successful).