Remove a useless #include of SelectorChecker.h

Rubber-stamped by Ryosuke Niwa.

* dom/DocumentStyleSheetCollection.cpp:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154209 268f45cc-cd09-0410-ab3c-d52691b4dbfc
<https://webkit.org/b/119536> Refactor highestEditableRoot to avoid a redundant call to rendererIsEditable

Reviewed by Benjamin Poulain.

Refactor highestEditableRoot to avoid an extra tree walk. We now walk up the ancestor chain up to
the first root editable element exactly once.

* dom/Node.cpp:
(WebCore::Node::rendererIsEditable): Change the order of conditions to make the evaluation faster
when we don't have to check RenderStyle's value.
* editing/htmlediting.cpp:
(WebCore::highestEditableRoot):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154212 268f45cc-cd09-0410-ab3c-d52691b4dbfc