Reviewed by Sam Weinig.

        The web process locks up when the plug-in process crashes
        https://bugs.webkit.org/show_bug.cgi?id=59999
        <rdar://problem/8889303>

        Add a hash map from plug-in paths to CoreIPC connections to PluginProcessConnectionManager.
        Add PluginProcessConnectionManager::pluginProcessCrashed and make it look up the corresponding
        CoreIPC connection and call postConnectionDidCloseOnConnectionWorkQueue on it.

        * Platform/CoreIPC/Connection.cpp:
        (CoreIPC::Connection::postConnectionDidCloseOnConnectionWorkQueue):
        * Platform/CoreIPC/Connection.h:
        * WebProcess/Plugins/PluginProcessConnectionManager.cpp:
        (WebKit::PluginProcessConnectionManager::getPluginProcessConnection):
        (WebKit::PluginProcessConnectionManager::removePluginProcessConnection):
        (WebKit::PluginProcessConnectionManager::pluginProcessCrashed):
        * WebProcess/Plugins/PluginProcessConnectionManager.h:
        * WebProcess/WebProcess.cpp:
        (WebKit::WebProcess::pluginProcessCrashed):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@85573 268f45cc-cd09-0410-ab3c-d52691b4dbfc