Restoring some of the functionality I removed in r19445. It's insufficient for
        each page to cancel keepAlive only for its child frames, because a frame
        can be removed from the page before we get a chance to cancel its keepAlive.
        So, the page destructor has to cancel keepAlive for all frames. This is safe
        because we prohibit closing a WebView while JavaScript is executing.

        * page/Frame.cpp:
        (WebCore::keepAliveSet):
        (WebCore::Frame::keepAlive):
        (WebCore::Frame::cancelAllKeepAlive):
        (WebCore::Frame::lifeSupportTimerFired):
        * page/Frame.h:
        * page/Page.cpp:
        (WebCore::Page::~Page):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@19468 268f45cc-cd09-0410-ab3c-d52691b4dbfc