Check visited color for visual diff.

Check visited color for visual diff.

The color which is actually used for painting needs to be checked when
figuring out if we need to do a paint invalidation. We are checking both
the color for :link and :visited so that the visited state is not exposed
through repaint timing.

This is a problem for other colors as well. If this approach is OK'ed,
I'll go ahead and fix the other ones.

BUG=439812
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=189918

[rune, 2015-02-10 00:09:01]

rune@opera.com changed reviewers:
+ wangxianzhu@chromium.org

[rune, 2015-02-10 00:09:01]

PTAL

[Timothy Loh, 2015-02-10 00:22:49]

On 2015/02/10 00:09:01, rune wrote:
> PTAL

Does this unintentionally expose visited link status (maybe via a timing
attack)? Maybe we'll want to check both visited and unvisited colors?

[rune, 2015-02-10 10:13:47]

rune@opera.com changed reviewers:
+ timloh@chromium.org

[rune, 2015-02-10 10:14:58]

On 2015/02/10 00:22:49, Timothy Loh wrote:
> On 2015/02/10 00:09:01, rune wrote:
> > PTAL
> 
> Does this unintentionally expose visited link status (maybe via a timing
> attack)? Maybe we'll want to check both visited and unvisited colors?

Well spotted. I've updated the patch and the description.

[Xianzhu, 2015-02-10 16:41:29]

lgtm

[rune, 2015-02-10 16:51:19]

The CQ bit was checked by rune@opera.com

[commit-bot: I haz the power, 2015-02-10 16:52:29]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/900443006/20001

[commit-bot: I haz the power, 2015-02-10 18:35:29]

Committed patchset #2 (id:20001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=189918