Auto merge of #381 - Mrowqa:capturing-js-stacks, r=jdm
Safe, straightforward API for capturing JS stacks
PR for https://github.com/servo/servo/issues/14987
Can someone take a look if it goes in the right direction and also look through my comments? Maybe, I have left some "stupid questions", but I wanted to post my changes and get feedback before weekend - I work from Europe, so here is middle of the night.
CC: @jdm
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