Avoid race in single thread suspension.

Don't allow more than one concurrent single thread suspension to avoid
potential cycles and deadlocks where threads try to suspend each other.
Bug: 16364458, 16354227

(cherry picked from commit f3d874c60ee3ada19ce26a5c4e532312b6f3a9e9)

Change-Id: I907f1d5591a6aa5c241d37d6b4a34f968f98df77
10 files changed