Build fix.

Add back the files to the Xcode project that were removed in r142580.

* WebKit2.xcodeproj/project.pbxproj:
* WebProcess/Plugins/PluginProcessConnectionManager.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142644 268f45cc-cd09-0410-ab3c-d52691b4dbfc