[HTML Imports] Employ load/error events to stabilize polling-based tests.

[HTML Imports] Employ load/error events to stabilize polling-based tests.

Now HTML Imports suppors load end error events, even inside the imported document.
Let's use it to make tests less flaky.

BUG=240592
R=dominicc,dglazkov

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=157583

[Hajime Morrita, 2013-09-10 09:09:43]

@dominicc: PTAL and cq?

[dominicc (has gone to gerrit), 2013-09-10 23:05:57]

On 2013/09/10 09:09:43, morrita1 wrote:
> @dominicc: PTAL and cq?

LGTM modulo one comment inline.

[dominicc (has gone to gerrit), 2013-09-10 23:06:30]

Pushed the wrong button... and here's the comment:

https://codereview.chromium.org/23903029/diff/1/LayoutTests/fast/dom/custom/r...
File LayoutTests/fast/dom/custom/registration-context-sharing.html (right):

https://codereview.chromium.org/23903029/diff/1/LayoutTests/fast/dom/custom/r...
LayoutTests/fast/dom/custom/registration-context-sharing.html:150:
t.step(function () {
You can use step_func for this.

[commit-bot: I haz the power, 2013-09-11 04:21:16]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/morrita@chromium.org/23903029/6001

[commit-bot: I haz the power, 2013-09-11 06:41:33]

Change committed as 157583