Add boot animation progress system property.

Test: m
Bug: 175686819
Change-Id: Ic2757054b908e2c7ff51e256e8683616df74fb33
diff --git a/init/reboot.cpp b/init/reboot.cpp
index 49baf9e..f4e12b9 100644
--- a/init/reboot.cpp
+++ b/init/reboot.cpp
@@ -655,6 +655,7 @@
 
         if (do_shutdown_animation) {
             SetProperty("service.bootanim.exit", "0");
+            SetProperty("service.bootanim.progress", "0");
             // Could be in the middle of animation. Stop and start so that it can pick
             // up the right mode.
             boot_anim->Stop();