Implement /content/ combinator.

Implement /content/ combinator.

spec: shadow styling
http://dev.w3.org/csswg/shadow-styling/#content-combinator

The added layout tests are basically the same as ::content's, because /content/ combinator should have almost the same behavior (except css text, ::content with descendant combinator).

BUG=349334
TEST=fast/dom/shadow/cascade-of-treeboundary-crossing-rules.html,fast/dom/shadow/content-combinator-css-text.html,fast/dom/shadow/content-combinator-dynamic-attribute-change.html,fast/dom/shadow/content-combinator-in-inert-shadow.html,fast/dom/shadow/content-combinator-scoped.html,fast/dom/shadow/content-combinator-with-cat.html,fast/dom/shadow/content-combinator-with-hat.html,fast/dom/shadow/content-combinator-with-host-pseudo-class-2.html,fast/dom/shadow/content-combinator-with-host-pseudo-class.html,fast/dom/shadow/content-combinator.html,fast/dom/shadow/multiple-content-combinator.html,fast/dom/shadow/no-style-sharing-with-uncommon-attribute-and-content-combinator.html

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=169085

[dglazkov, 2014-03-05 17:05:32]

Should we be removing ::content at the same time?

lgtm

[tasak, 2014-03-10 06:39:29]

Thank you for reviewing.

I created a new patch (including removing ::content).

However, the patch looks a little large.

So the patch size is ok?

If it is difficult to review / land, I will separate the patch into two patches,
one is adding /content/ and the other is removing ::content.

[tasak, 2014-03-10 08:18:50]

On 2014/03/10 06:39:29, tasak wrote:
> Thank you for reviewing.
> 
> I created a new patch (including removing ::content).
> 
> However, the patch looks a little large.
> 
> So the patch size is ok?
> 
> If it is difficult to review / land, I will separate the patch into two
patches,
> one is adding /content/ and the other is removing ::content.

I found that webkit_unit_tests uses ::content.

I removed RuleSetTest.findBestRuleSetAndAdd_DivWithContent and modified
CSSSelector.Representations.

[tasak, 2014-03-11 09:00:41]

Would you check the patch for removing ::content?

[dglazkov, 2014-03-11 16:31:29]

lgtm

[tasak, 2014-03-13 01:09:13]

The CQ bit was checked by tasak@google.com

[commit-bot: I haz the power, 2014-03-13 01:09:17]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tasak@google.com/187353003/110001

[commit-bot: I haz the power, 2014-03-13 04:32:59]

Change committed as 169085

[tasak, 2014-03-20 02:42:10]

A revert of this CL has been created in
https://codereview.chromium.org/205563004/ by tasak@google.com.

The reason for reverting is: Shadow DOM styling spec was changed.
/content/ was reverted in the spec.
.