Recently Chrome decided to stop supporting the NPAPI plug-in.
This plug-in basicly makes sure java can be ran in Chrome.
At this point they hid the option to enable it again,
How to enable it again:
1) open Chrome
2) Type chrome://flags/#enable-npapi in the adressbar
3) Enable the plug-in
4) Have fun playing runescape again in chrome.
Goodluck
Khaleesi