Fix a -Wsign-compare warning in adjustScopeMarkerForAdressSanitizer()

BUG=162783
R=ager@chromium.org

Review URL: https://codereview.chromium.org/273503006

git-svn-id: svn://svn.chromium.org/blink/trunk@173604 bbb929c8-8fbe-4397-9dbb-9b2b20218538