Reviewed by Kenneth Rohde Christiansen.

        [Qt] Use the QNetworkAccessManager zerocopy feature
        https://bugs.webkit.org/show_bug.cgi?id=50082

        The feature will be introduced in Qt 4.8.
        This patch is backwards compatible with Qt 4.7.

        * WebCore.pro:
        * platform/SharedBuffer.cpp:
        * platform/SharedBuffer.h:
        * platform/network/qt/QNetworkReplyHandler.cpp:
        (WebCore::QNetworkReplyHandler::QNetworkReplyHandler):
        (WebCore::QNetworkReplyHandler::bufferedData):
        (WebCore::QNetworkReplyHandler::sendResponseIfNeeded):
        (WebCore::QNetworkReplyHandler::downloadProgress):
        (WebCore::QNetworkReplyHandler::forwardData):
        (WebCore::QNetworkReplyHandler::start):
        * platform/network/qt/QNetworkReplyHandler.h:
        * platform/network/qt/ResourceHandleQt.cpp:
        (WebCore::ResourceHandle::supportsBufferedData):
        (WebCore::ResourceHandle::bufferedData):
        * platform/qt/SharedBufferQt.cpp:
        (WebCore::SharedBuffer::wrapQtByteBlock):
        (WebCore::SharedBuffer::hasPlatformData):
        (WebCore::SharedBuffer::platformData):
        (WebCore::SharedBuffer::platformDataSize):
        (WebCore::SharedBuffer::maybeTransferPlatformData):
        (WebCore::SharedBuffer::clearPlatformData):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@80551 268f45cc-cd09-0410-ab3c-d52691b4dbfc