Merge r172442 - [GTK] The plugins metadata cache doesn't work if the user cache directory doesn't exist
https://bugs.webkit.org/show_bug.cgi?id=135834

Reviewed by Philippe Normand.

Make sure the user cache directory exists. If creating the
directory fails for whatever reason, do not try to save the cache
to disk.

* UIProcess/Plugins/gtk/PluginInfoCache.cpp:
(WebKit::PluginInfoCache::PluginInfoCache):
(WebKit::PluginInfoCache::updatePluginInfo):

git-svn-id: http://svn.webkit.org/repository/webkit/releases/WebKitGTK/webkit-2.2@172444 268f45cc-cd09-0410-ab3c-d52691b4dbfc