**What steps will reproduce the problem?** 1. Check out the gist: https://gist.github.com/2945042 2. Notice I forget to add the SendPort in the mouse move handler (line 25) 3. Line 33 will fail as you'd expect with an un-set 'replyTo' 4. But, the Dartium tab crashes (not as you'd expect) **What is the expected output? What do you see instead?** Some helpful error message **What version of the product are you using? On what operating system?** 8832