stack traces are too long for test libraries

[mgiuffrida]

Here is the stack trace from calling MockInteractions.tap(foo.$$('div')), all the way to foo's on-tap handler. From this fiddle: https://jsfiddle.net/mgiuffrida/vb4rbt6t/

TypeError: Cannot set property 'innerText' of null
    at x-foo.myDivTapped (VM90:48)
    at HTMLDivElement.handler (VM77 polymer.html:516)
    at HTMLElement.fire (VM77 polymer.html:1280)
    at Object.fire (VM77 polymer.html:852)
    at Object.forward (VM77 polymer.html:1149)
    at Object.click (VM77 polymer.html:1134)
    at HTMLDivElement.handleNative (VM77 polymer.html:742)
    at makeMouseEvent (mock-interactions.js:139)
    at click (mock-interactions.js:228)
    at Object.tap (mock-interactions.js:302)
    at testTap (VM90:55)

11 functions is the bare mininum because the handler isn't calling other functions. But error.stack in error handlers will get truncated to 10 lines by default. Error.stackTraceLimit sets this limit, so it can be increased, but it's a sane default.

It would be nice if MockInteractions and/or Polymer event handlers involved fewer steps.