Blink needs %ErrorPrototype% in order to properly set up the inheritance
chain from DOMException, as specified in WebIDL:
https://heycam.github.io/webidl/#es-DOMException-specialness

This patch is similar to commit 5ec1cddc ("Expose %IteratorPrototype% as an
intrinsic in the public API"), with the difference that there was no entry
for %ErrorPrototype% in any of the mappings in contexts.h.

Bug: chromium:556950, chromium:737497
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: Iadc5b2b844f29f6c9640b6a89769d233931366e9
Reviewed-on: https://chromium-review.googlesource.com/559058Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Raphael Kubo da Costa (rakuco) <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#46464}