Expose the new function from the sigchainlib implementation. Google Bug 20217701 Google Change Id I7d21025595775e057ea703236ca88ceb07173136 Change-Id: Ie4bcb071f56097d44243cb97962d3bc13fe004ce Category: aosp improvement Domain: AOSP-Framework-CoreService Origin: 3rd-party Google Upstream-Candidate: no, proprietary Signed-off-by: Firefly <service@t-firefly.com>