Run an experiment like this:

1. start a large android app, for instance a game.  
2. switch back to Chrome, open lots of tabs that use large amounts of RAM (various Google properties i.e. inbox, cnn.com etc.)
3. watch the tab/app discard behavior.  Note that the android app is not killed, even though it's the LRU.

It may have something to do with the "visibility" attribute of the app.  A recent CL (still in transit) may help with this.