Remove Document::m_farmeElementsShouldIgnoreScrolling

This change removes m_frameElementsShouldIgnoreScrolling, which is no longer used.

TEST=none
BUG=none
R=haraken,tkent,hayato

Review URL: https://chromiumcodereview.appspot.com/17782002

git-svn-id: svn://svn.chromium.org/blink/trunk@153045 bbb929c8-8fbe-4397-9dbb-9b2b20218538