Reviewed by Martin Robinson.

        [GTK] Close connection when web process finishes
        https://bugs.webkit.org/show_bug.cgi?id=57540

        * Platform/CoreIPC/Connection.h:
        * Platform/CoreIPC/unix/ConnectionUnix.cpp:
        * Platform/PlatformProcessIdentifier.h: Use GPid as process
        identifier.
        * Platform/WorkQueue.h:
        * Platform/gtk/WorkQueueGtk.cpp:
        (WorkQueue::EventSource::EventSource): Add cancellable parameter.
        (WorkQueue::EventSource::cancel): New method to cancel the source.
        (WorkQueue::EventSource::performWorkOnTermination): New method to
        execute a work item called when child process has finished.
        (WorkQueue::registerEventSourceHandler): Create a GCancellable for
        the socket source.
        (WorkQueue::unregisterEventSourceHandler): Cancel the source
        instead of destroying it, this will cause the source to trigger
        with condition = 0, which makes the callback return FALSE and the
        source is destroyed.
        (WorkQueue::scheduleWorkOnSource): Pass NULL as cancellable for
        idle and timeout sources.
        (WorkQueue::scheduleWorkOnTermination): Create a child watch
        source to monitor the child process.
        * UIProcess/Launcher/gtk/ProcessLauncherGtk.cpp:
        (WebKit::ProcessLauncher::launchProcess): Use GPid instead of int
        as process identifier.
        * UIProcess/WebProcessProxy.cpp:
        (WebKit::WebProcessProxy::didFinishLaunching): Call
        WorkQueue::scheduleWorkOnTermination() for GTK platform too when
        web process has been launched.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@83280 268f45cc-cd09-0410-ab3c-d52691b4dbfc