Avoid livelock for a contended spinlock.
Avoid livelock for a contended spinlock.

I intend to replace the inc/dec based lock primitive with an atomic-test-and-set
primitive but for now, put out the fire.

BUG=270531
R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/27369002

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@159688 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs