DynamicPartitionControl: Add required_size to Prepare

Add out parameter required_size to PreparePartitionsForUpdate
to indicate the total size required on /userdata in order
to apply the update.

Bug: 138808058
Test: update_engine_unittests

Change-Id: I2768d13671e212fd24a1a22811b50c9738834459
diff --git a/common/dynamic_partition_control_stub.cc b/common/dynamic_partition_control_stub.cc
index bc792c8..974cd1b 100644
--- a/common/dynamic_partition_control_stub.cc
+++ b/common/dynamic_partition_control_stub.cc
@@ -43,7 +43,8 @@
     uint32_t source_slot,
     uint32_t target_slot,
     const DeltaArchiveManifest& manifest,
-    bool update) {
+    bool update,
+    uint64_t* required_size) {
   return true;
 }