Part of Bug 18208: Acid3 test 65 takes >33ms due to plugin refreshing
        on Windows
        <http://bugs.webkit.org/show_bug.cgi?id=18208>

        refresh() is now the only place where PluginPackages are instantiated.
        refresh() now asks for a set of plugins that no longer exist on disk,
        and the set of all plugin files in our plugin directories. Using these
        two sets we can update our instantiated plugins without copying any
        HashSets. The code in refresh() and in the platform-specific methods
        to crawl the filesystem is now quite a bit simpler.

        PluginDatabase now stores both a PluginSet and a HashMap that maps
        plugin paths to PluginPackages. This allows us to quickly determine
        whether we already have a PluginPackage instantiated for a particular
        path. The new add/remove methods handle the modification of these two
        collections.

        A nice side effect of all this is that refresh() no longer copies any
        HashSets.

        Reviewed by Mitz Pettel.

        * plugins/PluginDatabase.cpp:
        (WebCore::PluginDatabase::refresh): Unload any plugins that have been
        deleted from disk, and add any plugins that either weren't installed
        last time, or have changed since last time.
        (WebCore::PluginDatabase::getDeletedPlugins): Added.
        (WebCore::PluginDatabase::add): Added. Returns whether or not the
        PluginPackage was actually added to the database (duplicates won't be
        added).
        (WebCore::PluginDatabase::remove): Added.
        * plugins/PluginDatabase.h:
        * plugins/PluginPackage.h:
        (WebCore::PluginPackage::path): Added.
        (WebCore::PluginPackage::lastModified): Added.
        * plugins/gtk/PluginDatabaseGtk.cpp:
        (WebCore::PluginDatabase::getPluginPathsInDirectories): Renamed from
        getPluginsInDirectories. Now fills a HashSet of Strings instead of
        instantiated PluginPackages.
        * plugins/win/PluginDatabaseWin.cpp:
        (WebCore::addPluginPathsFromRegistry): Ditto.
        (WebCore::PluginDatabase::getPluginPathsInDirectories): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@31465 268f45cc-cd09-0410-ab3c-d52691b4dbfc