Make the Unix editing behavior the default.

The change removes unreachable code and does not actually change any behavior.

Review URL: https://chromiumcodereview.appspot.com/23895006

git-svn-id: svn://svn.chromium.org/blink/trunk@157777 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Extract ClipRect from RenderLayer.h to ClipRect.h

Review URL: https://chromiumcodereview.appspot.com/24066003

git-svn-id: svn://svn.chromium.org/blink/trunk@157778 bbb929c8-8fbe-4397-9dbb-9b2b20218538