GitLab

In some edge cases, these function may return nullptr which will crash
chrome.

TEST=passed unit tests and browser tests
BUG=1121330

Change-Id: I4863ac4a43b5dcdae684f948abbf40d627c4ab9f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2462745Reviewed-by: Darren Shen <shend@chromium.org>
Commit-Queue: Jing Wang <jiwan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#815444}