Tests asynchronous call stacks for scripted scroll events.

Set timer for test function.
Captured call stacks in no particular order:
Call stack:
    0) onScroll1 (async-callstack-scripted-scroll.js:37)
    [scroll]
    0) timeout (async-callstack-scripted-scroll.js:29)
    [setTimeout]
    0) testFunction (async-callstack-scripted-scroll.js:20)
    [setTimeout]
    0) scheduleTestFunction <omitted>
    <... skipped remaining frames ...>

Call stack:
    0) onScroll2 (async-callstack-scripted-scroll.js:44)
    [scroll]
    0) timeout (async-callstack-scripted-scroll.js:29)
    [setTimeout]
    0) testFunction (async-callstack-scripted-scroll.js:20)
    [setTimeout]
    0) scheduleTestFunction <omitted>
    <... skipped remaining frames ...>