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

Revert of De-flaking some tests in virtual/gpu/fast/canvas (patchset #6 id:100001 of https://codereview.chromium.org/1161463007/)

Reason for revert:
Caused one odd consistent failure :(

junov will look into it tomorrow.

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=virtual%2Fgpu%2Ffast%2Fcanvas%2FtoDataURL-alpha.html&testType=layout-tests

Original issue's description:
> 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

TBR=senorblanco@chromium.org,junov@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=410929
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=196535

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

Created Revert of De-flaking some tests in virtual/gpu/fast/canvas

[commit-bot: I haz the power, 2015-06-04 22:32:18]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1167013003/1

[commit-bot: I haz the power, 2015-06-04 22:33:10]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=196535