Remove Position::findParent, all it does is call parentNode()

There's no reason to put a method wrapper around calling parentNode(), just
eliminate this method. I also renamed a bunch of local variables and refactored
the functions to be more modern and simplify the code.

Review URL: https://chromiumcodereview.appspot.com/23533031

git-svn-id: svn://svn.chromium.org/blink/trunk@157215 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add validator for "Frames to capture" setting

Added a validator that ensures the value is an integer from specified range.

BUG=None

Review URL: https://chromiumcodereview.appspot.com/23578011

git-svn-id: svn://svn.chromium.org/blink/trunk@157216 bbb929c8-8fbe-4397-9dbb-9b2b20218538