Simplify CSSSelector::isAttributeSelector() by not checking each Match type

Simplify CSSSelector::isAttributeSelector() by not checking each Match type
explicitly and reordering the Match enum instead so that the attribute
selector match type are contiguous and at the end of the enum. This way, the
check can become (m_match >= FirstAttributeSelectorMatch).

This optimization is similar to the one we already use in CollectionType.h
for collection types. isAttributeSelector() is called from
SelectorChecker::checkOne() which is hot code.

I see a ~2% progression on Dromaeo's cssquery-jquery:
http://dromaeo.com/?id=222514,222518

Review URL: https://codereview.chromium.org/315043005

git-svn-id: svn://svn.chromium.org/blink/trunk@175632 bbb929c8-8fbe-4397-9dbb-9b2b20218538