Add FrameLoader::policyDocumentLoader, and change
        provisionalDocumentLoader to have a const signature to be
        consistent with documentLoader and activeDocumentLoader.

        * WebCore.base.exp:
        * WebCore.order:
        * loader/FrameLoader.cpp:
        (WebCore::FrameLoader::policyDocumentLoader):
        (WebCore::FrameLoader::provisionalDocumentLoader):
        * loader/FrameLoader.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@32320 268f45cc-cd09-0410-ab3c-d52691b4dbfc