Use concurrent GC in PackageManagerService constructor.

We don't have a hard dependency on GC completion anyway.

Change-Id: Iff7dc1b35e1a128238ea088a806bef377299f172
Fixes: 170408071
Test: presubmit

services/core/java/com/android/server/pm/PackageManagerService.java

@@ -3842,7 +3842,7 @@ public class PackageManagerService extends IPackageManager.Stub
         // are all flushed.  Not really needed, but keeps things nice and
         // tidy.
         t.traceBegin("GC");
-        Runtime.getRuntime().gc();
+        VMRuntime.getRuntime().requestConcurrentGC();
         t.traceEnd();
 
         // The initial scanning above does many calls into installd while