Make userspace_reboot.in_progress sysprop-as-api

sys.init.userspace_reboot.in_progress will be used to notify all
the processes (including vendor ones) that userspace reboot is
happening, hence it should be treated as stable public api.

All other sys.init.userspace_reboot.* props will be internal to /system
partition and don't require any stability guarantees.

Test: builds
Test: adb reboot userspace
Bug: 135984674
Change-Id: Ifb64a6bfae2de76bac67edea68df44e33c9cfe2d
diff --git a/init/reboot.cpp b/init/reboot.cpp
index 7167672..13cebcc 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -38,6 +38,7 @@
 #include <thread>
 #include <vector>
 
+#include <InitProperties.sysprop.h>
 #include <android-base/chrono_utils.h>
 #include <android-base/file.h>
 #include <android-base/logging.h>
@@ -743,8 +744,8 @@
     // actions. We should make sure, that all of them are propagated before
     // proceeding with userspace reboot. Synchronously setting kUserspaceRebootInProgress property
     // is not perfect, but it should do the trick.
-    if (property_set(kUserspaceRebootInProgress, "1") != 0) {
-        return Error() << "Failed to set property " << kUserspaceRebootInProgress;
+    if (!android::sysprop::InitProperties::userspace_reboot_in_progress(true)) {
+        return Error() << "Failed to set sys.init.userspace_reboot.in_progress property";
     }
     EnterShutdown();
     std::vector<Service*> stop_first;