[M65] Add sleep fallback to base::SpinLock.

This avoids a situation where a thread of lesser priority is holding the
lock while a bunch of higher priority threads hog all CPU spinning,
preventing the lesser priority thread from releasing the lock.

Bug: 758695, 770312
Change-Id: Ibf36f16023069e32f3f55716a2b63e47fff0d9f7
Reviewed-on: https://chromium-review.googlesource.com/873647
Commit-Queue: Max Morin <maxmorin@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Chris Palmer <palmer@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#530835}(cherry picked from commit da57669f62bed877ec39dd5847470592109cb405)
Reviewed-on: https://chromium-review.googlesource.com/928481
Reviewed-by: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/branch-heads/3325@{#529}
Cr-Branched-From: bc084a8b5afa3744a74927344e304c02ae54189f-refs/heads/master@{#530369}
1 file changed