Chrome Version: (copy from chrome://version)
OS: (e.g. Win7, OSX 10.9.5, etc...)

What steps will reproduce the problem?
(1) Evaluate some command in the console that takes a long time, e.g.
`
var start = performance.now(); for (var i=0; i<100000000; i++) {x = performance.now() - start}
`

(2) Type more things in the console prompt and press enter

What is the expected result?
User should not be surprised that pressing enter has no effect.

What happens instead?
Pressing enter has no effect.  DevTools UI is not blocked, but no further console commands can be sent because it's waiting.

Perhaps we could have a wait/loading spinner to indicate this state?