Upon load failure, remove sync script from execution queue.

Upon load failure, remove sync script from execution queue.

If a script element is to be loaded synchronously and executed in order,
it's queued for execution before loading. Should that load fail, the
immediate execution of the script,

  https://html.spec.whatwg.org/#execute-the-script-block

should only result in an error event being dispatched.

Implementation-wise, along with signalling error, the failed script must also
be removed from the internal in-order execution queue. We're done with
(not) executing the script and failure to remove it will cause subsequent
processing of the script execution queue to see the script as having failed
to load and re-dispatch an error event.

R=haraken
BUG=503077

Review URL: https://codereview.chromium.org/1263743002

git-svn-id: svn://svn.chromium.org/blink/trunk@199656 bbb929c8-8fbe-4397-9dbb-9b2b20218538