Tests asynchronous call stacks for XHRs.

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Set timer for test function.
Captured call stacks in no particular order:
Call stack:
    0) downloadEnd (async-callstack-xhrs.html:36)
    1) sendXHR (async-callstack-xhrs.html:60)
    2) sendSyncXHR (async-callstack-xhrs.html:21)
    3) timeout (async-callstack-xhrs.html:16)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) downloadEnd (async-callstack-xhrs.html:36)
    [XMLHttpRequest.send]
    0) sendXHR (async-callstack-xhrs.html:60)
    1) sendAsyncXHR (async-callstack-xhrs.html:20)
    2) timeout (async-callstack-xhrs.html:17)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) downloadProgress (async-callstack-xhrs.html:45)
    [XMLHttpRequest.send]
    0) sendXHR (async-callstack-xhrs.html:60)
    1) sendAsyncXHR (async-callstack-xhrs.html:20)
    2) timeout (async-callstack-xhrs.html:17)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) uploadEnd (async-callstack-xhrs.html:41)
    [XMLHttpRequest.send]
    0) sendXHR (async-callstack-xhrs.html:60)
    1) sendAsyncXHR (async-callstack-xhrs.html:20)
    2) timeout (async-callstack-xhrs.html:17)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) uploadProgress (async-callstack-xhrs.html:50)
    [XMLHttpRequest.send]
    0) sendXHR (async-callstack-xhrs.html:60)
    1) sendAsyncXHR (async-callstack-xhrs.html:20)
    2) timeout (async-callstack-xhrs.html:17)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) xhr.onreadystatechange (async-callstack-xhrs.html:30)
    1) sendXHR (async-callstack-xhrs.html:60)
    2) sendSyncXHR (async-callstack-xhrs.html:21)
    3) timeout (async-callstack-xhrs.html:16)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

Call stack:
    0) xhr.onreadystatechange (async-callstack-xhrs.html:30)
    [XMLHttpRequest.send]
    0) sendXHR (async-callstack-xhrs.html:60)
    1) sendAsyncXHR (async-callstack-xhrs.html:20)
    2) timeout (async-callstack-xhrs.html:17)
    [setTimeout]
    0) testFunction (async-callstack-xhrs.html:11)

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