Fix aggressive RELEASE_ASSERTs in Resource

I added RELEASE_ASSERTs in my last patch what are found to be too
aggressive. Change them back to ASSERTs and add preventive measures.

BUG=352043
R=japhet@chromium.org

Review URL: https://codereview.chromium.org/243533002

git-svn-id: svn://svn.chromium.org/blink/trunk@171972 bbb929c8-8fbe-4397-9dbb-9b2b20218538