Made SelectorChecker::match to return matched selector's specificity for :host.
    
The specificity of a :matches() pseudo-class is the specificity of the most specific complex selector that matched.
c.f. http://www.w3.org/TR/selectors4/#specificity
    
:host() pseudo-class works in almost the same way as :matches().
So the specificity of :host() pseudo-class should be the specificity of the most specific complex selector that matched.
    
To do so, CSSSelector::specificity ignores :host() pseudo-class and SelectorChecker calculates :host()'s specificity.
(c.f. the spec says :not() or :matches() pseudo-class itself does not contribute any additional specificity)
    
When comparing matched rules, see both CSSSelector::specificity() and specificity calculated by SelectorChecker::match().
    
BUG=320697
TEST=fast/dom/shadow/host-pseudo-class.html

Review URL: https://codereview.chromium.org/76063003

git-svn-id: svn://svn.chromium.org/blink/trunk@162785 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Disable DidWriteToInitialDocumentBeforeModalDialog on Windows.

Like DidAccessInitialDocumentBodyBeforeModalDialog, this test appears to
be failing only on the WebKit XP (deps) bot.

BUG=312192

Review URL: https://codereview.chromium.org/88423004

git-svn-id: svn://svn.chromium.org/blink/trunk@162786 bbb929c8-8fbe-4397-9dbb-9b2b20218538