gistfile1.txt

Notation:
  f -> g                "f calls g"
  f -> (a -> b) g:      "f calls g, supplying async parent stack a -> b"


Suppose we have:

    /* in chrome */
1:  function contentVisibleChromeImplementedInJS(...) {
2:    var p0 = Promise((f0, r0) => { ... });
3:    var p1 = p0.then(f1, r1);
      return p1;
    }

    /* in content */
4:  let p1 = contentVisibleChromeImplementedInJS(...)
5:  var p2 = p1.then(f2, r2);


p0 captures '4 -> 2' as its saved stack
p1 captures '4 -> 3' as its saved stack.
p2 captures '5' as its saved stack.

Promise event handlers are invoked in their own event ticks: the event loop
calls some promise machinery which passes the value to the handler, so the
handler's true call stack looks like: eventLoop -> promiseImpl -> handler.

When invoking a resolution handler, a promise attaches its saved stack as the
handler call's async parent. p0's handler is f1, so p0 will call f1 with an
async parent of '4 -> 2'; the whole stack is thus: eventLoop -> promiseImpl ->
(4 -> 2) handler.

An error in f1 would capture the stack 'eventloop -> promiseImpl -> (4 -> 2) f1'

so if f1 creates and throws exception ex, ex.stack should be 'eventLoop -> promiseImpl -> (4 -> 2) f1'
unfiltered, or '4' filtered.