Add cli option to enable multi-threaded compression

Test: update_device.py --enable-threading, make sure threading is being
turned on

Change-Id: I1d0e5ab5c2e65cc48b5126fb186f770b68188351
diff --git a/aosp/update_attempter_android.cc b/aosp/update_attempter_android.cc
index 617edab..ea0b0d9 100644
--- a/aosp/update_attempter_android.cc
+++ b/aosp/update_attempter_android.cc
@@ -350,6 +350,12 @@
   if (!headers[kPayloadDisableVABC].empty()) {
     install_plan_.disable_vabc = true;
   }
+  if (!headers[kPayloadEnableThreading].empty()) {
+    install_plan_.enable_threading = true;
+  }
+  if (!headers[kPayloadBatchedWrites].empty()) {
+    install_plan_.batched_writes = true;
+  }
 
   BuildUpdateActions(fetcher);