Support invalidation sets for :host pseudo.

Support invalidation sets for :host pseudo.

Traverse the selectorList() for :host pseudo, extract features, and create
class invalidation sets like we do for features and classes on the top level.

Supporting invalidation sets for :host is a prerequisite for optimizing style
recalc for the "active" attribute in issue 339729. The next step is to
support invalidation sets for attributes.

R=esprehn@chromium.org, chrishtr@chromium.org
BUG=335247, 339729

[chrishtr, 2014-03-21 21:40:23]

lgtm

[ojan, 2014-03-22 00:32:23]

lgtm

A bunch of cosmetic nits.

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature.cpp
File Source/core/css/RuleFeature.cpp (right):

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:124: if (list) {
Nit: typically we write this as follows: 
if (const CSSSelectorList* list = component->selectorList()) {

In addition to being one line, it has the advantage of scoping the variable to
the contents of the if-statement.

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:177: if (!current || !(current =
current->tagHistory()))
Nit: In contrast to the above case, I find setting current inside the
if-statement confusing. It looks like a typo. I can see that it's not by
inspecting the code closely.

The difference with the above case IMO is the type. The type means it would be a
compiler error if you change the = to an ==.

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:193: if (list)
Ditto first comment.

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:217: if  (current->selectorList())
Nit: extra space after the if.

[esprehn, 2014-03-22 01:25:34]

not lgtm, this patch is not correct as is. :host() can definitely have more than
one argument.

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature.cpp
File Source/core/css/RuleFeature.cpp (right):

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:125: ASSERT(list->hasOneSelector());
Why does this have to have one selector? You can write host(a, b)

https://codereview.chromium.org/208013002/diff/1/Source/core/css/RuleFeature....
Source/core/css/RuleFeature.cpp:177: if (!current || !(current =
current->tagHistory()))
Don't do assignments inside || or &&

[rune, 2014-03-24 11:27:34]

Re-submitted as:

https://codereview.chromium.org/209333005/

Closing.