Merge webkit.org at r54127 : Make FLATTEN_IFRAME method overrides protected

Merge webkit.org at r54127 : Make FLATTEN_IFRAME method overrides protected

RenderPartObject inherits calcWidth/calcHeight as public methods throught the
chain RenderPart -> RenderWidget -> RenderReplaced -> RenderBox.

On Android, RenderPartObject overrides calcWidth/calcHeight as private methods
for FLATTEN_IFRAME. This is not yet upstreamed.

The new WebKit uses calcWidth/calcHeight from RenderEmbeddedObject, which
inherits from RenderPartObject. So we need to make the these methods protected
in RenderPartObject

Change-Id: Ifb48d5daa10fc14c80f6da987cbd034713febc12