De-flaking some tests in virtual/gpu/fast/canvas

De-flaking some tests in virtual/gpu/fast/canvas

This change uses layoutAndPaintAsyncThen + notifyDone to fix the
flakiness of some canvas layout tests with gpu acceleration enabled.
This approach seems to do the trick locally. This change fixes a
subset of the tests to see if this approach holds up on the test bots.
If it does, the rest of the tests will be fixed in a follow-up change.

BUG=410929
NOTRY=true

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196523

[Justin Novosad, 2015-06-04 04:45:38]

junov@chromium.org changed reviewers:
+ senorblanco@chromium.org

[Justin Novosad, 2015-06-04 04:45:39]

PTAL

[Stephen White, 2015-06-04 15:34:32]

LGTM but if this is required in all cases, shouldn't we change the
implementation of notifyDone() instead? Are there tests for which that would be
overkill?

[Justin Novosad, 2015-06-04 18:05:24]

The CQ bit was checked by junov@chromium.org

[Justin Novosad, 2015-06-04 18:05:24]

The patchset sent to the CQ was uploaded after l-g-t-m from
senorblanco@chromium.org
Link to the patchset: https://codereview.chromium.org/1161463007/#ps60001
(title: "plus rebaseline")

[commit-bot: I haz the power, 2015-06-04 18:05:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1161463007/60001

[Justin Novosad, 2015-06-04 19:05:11]

The CQ bit was checked by junov@chromium.org

[Justin Novosad, 2015-06-04 19:05:11]

The patchset sent to the CQ was uploaded after l-g-t-m from
senorblanco@chromium.org
Link to the patchset: https://codereview.chromium.org/1161463007/#ps100001
(title: "undo previous patch (wrong issue)")

[commit-bot: I haz the power, 2015-06-04 19:05:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1161463007/100001

[commit-bot: I haz the power, 2015-06-04 19:09:40]

Committed patchset #6 (id:100001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196523

[leviw_travelin_and_unemployed, 2015-06-04 22:31:36]

A revert of this CL (patchset #6 id:100001) has been created in
https://codereview.chromium.org/1167013003/ by leviw@chromium.org.

The reason for reverting is: Caused one odd consistent failure :(

junov will look into it tomorrow.

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=vir....