Have detached ScriptLoaders detach their PendingScripts.

A ScriptLoader that has become detached from its document will not
execute the script once the script resource has loaded.

If in such a detached state, make sure the ScriptLoader lets go
of its PendingScript promptly.

R=
BUG=

Review-Url: https://codereview.chromium.org/2028613002
Cr-Commit-Position: refs/heads/master@{#397106}
1 file changed