SurfaceFlinger: Shared timeline plumbing

Add plumbing to get shared timeline data from Surface Flinger to HWUI
and back.

Bug: 162890382
Bug: 162888881

Test: SF unit tests
Change-Id: Ifb76e6bf28d43c051e6c8ff568437ec9a106b865
diff --git a/services/surfaceflinger/Layer.cpp b/services/surfaceflinger/Layer.cpp
index eced6bd..152c044 100644
--- a/services/surfaceflinger/Layer.cpp
+++ b/services/surfaceflinger/Layer.cpp
@@ -1435,6 +1435,10 @@
     return true;
 }
 
+void Layer::setFrameTimelineVsync(int64_t frameTimelineVsyncId) {
+    mFrameTimelineVsyncId = frameTimelineVsyncId;
+}
+
 Layer::FrameRate Layer::getFrameRateForLayerTree() const {
     const auto frameRate = getDrawingState().frameRate;
     if (frameRate.rate > 0 || frameRate.type == FrameRateCompatibility::NoVote) {