Revert "Revert "installd: Fix set dex2oat to background after boot_complete""

This reverts commit 633e1fbfedac66919a1e960640aa29376dd886dd.

Bug: 175381211
Reason for revert: b/175381211 should be resolved after omg/25953 fixed

Change-Id: I494ccc485ab5a125ba2a92064c0ee33e7fb6d2e6
diff --git a/cmds/installd/dexopt.cpp b/cmds/installd/dexopt.cpp
index 594880a..65fc46e 100644
--- a/cmds/installd/dexopt.cpp
+++ b/cmds/installd/dexopt.cpp
@@ -1818,10 +1818,13 @@
 
     pid_t pid = fork();
     if (pid == 0) {
+        // Need to set schedpolicy before dropping privileges
+        // for cgroup migration. See details at b/175178520.
+        SetDex2OatScheduling(boot_complete);
+
         /* child -- drop privileges before continuing */
         drop_capabilities(uid);
 
-        SetDex2OatScheduling(boot_complete);
         if (flock(out_oat.fd(), LOCK_EX | LOCK_NB) != 0) {
             PLOG(ERROR) << "flock(" << out_oat.path() << ") failed";
             _exit(DexoptReturnCodes::kFlock);