Don't zero out memory added to a free list if ASan is enabled

This CL fixes a regression caused by r177304.

BUG=390936

Review URL: https://codereview.chromium.org/363173002

git-svn-id: svn://svn.chromium.org/blink/trunk@177444 bbb929c8-8fbe-4397-9dbb-9b2b20218538
LeakExpectations: Add viewsource-6 as a WONTFIX

NOTRY=true
TBR=hajimehoshi
BUG=364398

Review URL: https://codereview.chromium.org/369673005

git-svn-id: svn://svn.chromium.org/blink/trunk@177445 bbb929c8-8fbe-4397-9dbb-9b2b20218538