Prepare pass_through mounts

Execute mkdir -p /mnt/pass_through/0/emulated
and bootstrap the emulated volume for user 0.

The 'pass_through' paths allow us bind mount the lower
filesystem directly into /storage, bypassing any sdcardfs
of FUSE mounts.

This change is part of enabling upcoming platform changes that are
described in the bug linked below.

Bug: 135341433
Test: builds, boots and pass through directories are created
Change-Id: I46ce207d06a1ec550b8bacac259387371fc0b841
diff --git a/rootdir/init.rc b/rootdir/init.rc
index d5fed5a..0fa6efc 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -154,6 +154,14 @@
     mkdir /mnt/user/0/self 0755 root root
     mkdir /mnt/user/0/emulated 0755 root root
     mkdir /mnt/user/0/emulated/0 0755 root root
+
+    # Prepare directories for pass through processes
+    mkdir /mnt/pass_through 0755 root root
+    mkdir /mnt/pass_through/0 0755 root root
+    mkdir /mnt/pass_through/0/self 0755 root root
+    mkdir /mnt/pass_through/0/emulated 0755 root root
+    mkdir /mnt/pass_through/0/emulated/0 0755 root root
+
     mkdir /mnt/expand 0771 system system
     mkdir /mnt/appfuse 0711 root root
 
@@ -678,6 +686,8 @@
   # Mount default storage into root namespace
   mount none /mnt/user/0 /storage bind rec
   mount none none /storage slave rec
+  # Bootstrap the emulated volume for the pass_through directory for user 0
+  mount none /data/media /mnt/pass_through/0/emulated bind rec
 on zygote-start && property:persist.sys.fuse=false
   # Mount default storage into root namespace
   mount none /mnt/runtime/default /storage bind rec