Tests asynchronous call stacks for fetch.

Set timer for test function.
Captured call stacks in no particular order:
Call stack:
    0) chained1 (async-callstack-fetch.js:20)
    [Promise.then]
    0) doFetch (async-callstack-fetch.js:19)
    [setTimeout]
    0) testFunction (async-callstack-fetch.js:14)
    [setTimeout]
    0) scheduleTestFunction <omitted>
    <... skipped remaining frames ...>

Call stack:
    0) chained4 (async-callstack-fetch.js:24)
    [Promise.then]
    0) doFetch (async-callstack-fetch.js:23)
    [setTimeout]
    0) testFunction (async-callstack-fetch.js:14)
    [setTimeout]
    0) scheduleTestFunction <omitted>
    <... skipped remaining frames ...>