Now when Chrome is 64-bits, how do I install the Java plugin? As long as Chrome just was 32 bit, the Java plugin was not supported since Java for Mac OS X is 64 bit but now when Chrome (since version 39) is 64 bit, how do I install/enable the Java plugin?

Googling just returns old results such as

https://java.com/en/download/faq/chrome.xml (that refers to this blog post http://blog.chromium.org/2014/08/mac-chrome-when-im-sixty-four-bits.html)

https://support.google.com/chrome/answer/2429779?hl=en (talking about Java 7, I have Java 8).
You can download the latest version of Java, install, and reboot, and it should be listed in chrome://plugins. Make sure that it's enabled (there should be a button saying Disable):


Note: You probably want to check Always allowed because Java always pops up and asks you if you want  it to run.

Once you finish this, you can test java.