Suppress cancellation notification in XMLHttpRequest::endLoading

We call ThreadableLoader::cancel in XMLHttpRequest::endLoading as it
is required by ThreadableLoader, but that cancellation should not be
notified to JS. Otherwise, the script can replace |m_loader| in the
XMLHttpRequest instance and that violates the ThreadableLoader assumption
itself.

BUG=638567, 638432

Review-Url: https://codereview.chromium.org/2271033003
Cr-Commit-Position: refs/heads/master@{#414026}
1 file changed