There's a huge section of Aura-only tests in the middle of site_per_process_browsertest.cc, which is a multi-thousand line file.  This makes it confusing to tell which tests run on which platforms.  (Just noticed it as new Aura-only tests were being added in https://codereview.chromium.org/2034213002/.)

We should move these out into an Aura specific test file, to make it clear which test coverage we're missing on other platforms like Mac (and to make the file a bit smaller).

Alex, would you be willing to split this out when you get a chance?  (I'm mainly picking you because so much of the team is OOO at the moment, so feel free to find another owner.)  :)