Fix use-after-delete in ParseContext.cpp. This bug was exposed after a refactoring from the translator. BUG=None TEST=angle_unittests,angle_end2end_tests Change-Id: I13fddcbe84f87826068a557f139f6e35c674571e Reviewed-on: https://chromium-review.googlesource.com/287832 Reviewed-by: Zhenyao Mo <zmo@chromium.org> Tested-by: Jamie Madill <jmadill@chromium.org>