Selection code spends a lot of time in InlineTextBox::localSelectionRect
https://bugs.webkit.org/show_bug.cgi?id=113364

Reviewed by Enrica Casucci.

Avoid computing the font width when we're selecting the entire line box.

This appears to be 25-26% improvement on Interactive/SelectAll:Time.

* rendering/InlineTextBox.cpp:
(WebCore::InlineTextBox::localSelectionRect):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147008 268f45cc-cd09-0410-ab3c-d52691b4dbfc