add asserts around results from requestLock (patchset #3 id:40001 of https://codereview.chromium.org/1155403003/)"

This reverts commit 3953d360417655b8000df0951699121383db45c3.

BUG=skia:
TBR=

Review URL: https://codereview.chromium.org/1165583005
3 files changed