<rdar://problem/5640615> REGRESSION (Safari 2-3): Changing subframe encoding rules broke
        some sites.

        Other browsers' behavior keeps changing; let's implement what Firefox and Opera do now:
        if the frame and subframe belong to the same site, then the encoding is inherited from parent
        frame to subframe. Otherwise, it is not.

        Always inheriting the encoding would cause a security problem.

        Tests: http/tests/misc/frame-default-enc-different-domain.html
               http/tests/misc/frame-default-enc-same-domain.html
               fast/encoding/frame-default-enc.html

        * loader/FrameLoader.cpp:
        (WebCore::FrameLoader::write): Also removed a check for m_frame->document() being non-null -
        this function also has code that uses it without checking, so it must be safe.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@30986 268f45cc-cd09-0410-ab3c-d52691b4dbfc