Ensure objects emitted in code are allocated in old space.

runtime/vm/assembler.cc

Index: runtime/vm/assembler.cc
diff --git a/runtime/vm/assembler.cc b/runtime/vm/assembler.cc
index 446c78a630fae243ffe381828c8a327a0d0b97fd..794f937783c96b85f4949c02f499b77478c39427 100644
--- a/runtime/vm/assembler.cc
+++ b/runtime/vm/assembler.cc
@@ -148,6 +148,7 @@ void AssemblerBuffer::EmitObject(const Object& object) {
   // Since we are going to store the handle as part of the fixup information
   // the handle needs to be a zone handle.
   ASSERT(object.IsZoneHandle());
+  ASSERT(object.IsOld());
   EmitFixup(new PatchCodeWithHandle(pointer_offsets_, object));
   cursor_ += kWordSize;  // Reserve space for pointer.
 }