To me, it looks like they are allowing https @ plus.google.com, plus.sandbox.google.com, ssl.gstatic.com, talk.google.com, talkgadget.google.com, and ssl.gstatic.com to use WebUIs (most likely Dart web apps) [1] and NaCl [2].

  // Temporarily allow these whitelisted apps and WebUIs to use NaCl.

> Google Native Client (NaCl) is a sandboxing technology for running a subset of Intel x86 or ARM native code in a sandbox. It is proposed for safely running native code from a web browser, allowing web-based applications to run at near-native speeds,[2] which aligns well with Google's plans with Chrome OS. It may also be used for securing browser plugins, and in the future parts of other applications or full applications. [2]

[1] https://www.dartlang.org/articles/web-ui/

[2] http://en.wikipedia.org/wiki/Google_Native_Client