Frame unique names now avoid collisions in practice in default Chrome, unless a renderer process is exploited.  In OOPIF-enabled modes like --isolate-extensions or --site-per-process, it's still possible to get a collision if two iframes in different processes race to create the same name.

We should move unique name computation from Blink's FrameTree.cpp to the browser process to make them trustworthy.

See also  issue 588800  (where r397443 prevented common collisions),  issue 523372  (for concerns about unique name length), and issue 558680 (for the consequences of a collision, which include renderer kills due to mismatched URL and origin).