Minor cleanups of invalidation code.

The RenderBox::repaintDuringLayoutIfMoved() method is no-longer used since
the old repaint path was deleted. This CL removes it and renames the
repaintOverhaningFloats() method to be invalidatePaintForOverhangingFloats().

Review URL: https://codereview.chromium.org/336073005

git-svn-id: svn://svn.chromium.org/blink/trunk@177021 bbb929c8-8fbe-4397-9dbb-9b2b20218538