Reviewed by Kent Tamura.

        Change filenameFromString to return CString
        https://bugs.webkit.org/show_bug.cgi?id=39494

        filenameFromString returns a newly allocated string and the caller must
        free the string. GTK and EFL ports use g_free while all others ports use
        fastFree. This is confusing because the same function behaves
        differently with respect to ports. Change filenameFromString to return
        CString.

        * platform/FileSystem.cpp:
        (WebCore::filenameFromString):
        * platform/FileSystem.h:
        * platform/efl/FileSystemEfl.cpp:
        (WebCore::filenameFromString):
        * platform/gtk/FileChooserGtk.cpp:
        (WebCore::FileChooser::basenameForWidth):
        * platform/gtk/FileSystemGtk.cpp:
        (WebCore::filenameFromString):
        (WebCore::filenameForDisplay):
        (WebCore::fileExists):
        (WebCore::deleteFile):
        (WebCore::deleteEmptyDirectory):
        (WebCore::getFileSize):
        (WebCore::getFileModificationTime):
        (WebCore::makeAllDirectories):
        (WebCore::pathGetFileName):
        (WebCore::directoryName):
        (WebCore::listDirectory):
        * platform/gtk/SharedBufferGtk.cpp:
        (WebCore::SharedBuffer::createWithContentsOfFile):
        * platform/network/soup/ResourceHandleSoup.cpp:
        (WebCore::startHttp):
        * platform/posix/SharedBufferPOSIX.cpp:
        (WebCore::SharedBuffer::createWithContentsOfFile):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@60668 268f45cc-cd09-0410-ab3c-d52691b4dbfc