Avoid using instanceRoot in layout tests

Avoid using instanceRoot in layout tests

Avoid using instanceRoot in layout tests, instead get the correspong element directly by using getElementById.

BUG=313438
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173827

[rwlbuis, 2014-05-10 21:29:26]

PTAL. I am converting these tests as they can't work when instanceRoot is
removed but the tests are still useful.

[pdr., 2014-05-10 21:31:56]

On 2014/05/10 21:29:26, rwlbuis wrote:
> PTAL. I am converting these tests as they can't work when instanceRoot is
> removed but the tests are still useful.

LGTM

[rwlbuis, 2014-05-10 21:39:39]

The CQ bit was checked by rob.buis@samsung.com

[commit-bot: I haz the power, 2014-05-10 21:39:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rob.buis@samsung.com/278033003/1

[commit-bot: I haz the power, 2014-05-10 22:23:56]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  win_blink_rel on tryserver.blink
(http://build.chromium.org/p/tryserver.blink/builders/win_blink_rel/builds/6877)

[commit-bot: I haz the power, 2014-05-10 23:15:45]

Change committed as 173827