VM: Materialize stub pc-markers (smi 0) eagerly on deoptimization.

runtime/vm/deferred_objects.cc

Index: runtime/vm/deferred_objects.cc
diff --git a/runtime/vm/deferred_objects.cc b/runtime/vm/deferred_objects.cc
index a647af1768a356b2db103551cd94df8463f4cd59..7a0b08e975e51c610d0695c14fdf2e6b0db351cd 100644
--- a/runtime/vm/deferred_objects.cc
+++ b/runtime/vm/deferred_objects.cc
@@ -161,11 +161,8 @@ void DeferredPcMarker::Materialize(DeoptContext* deopt_context) {
   uword* dest_addr = reinterpret_cast<uword*>(slot());
   Function& function = Function::Handle(zone);
   function ^= deopt_context->ObjectAt(index_);
-  if (function.IsNull()) {
-    // Callee's PC marker is not used (pc of Deoptimize stub). Set to 0.
-    *dest_addr = 0;
-    return;
-  }
+  // Null case is already handled in DeoptPcMarkerInstr::Execute.
+  ASSERT(!function.IsNull());
   const Error& error = Error::Handle(zone,
       Compiler::EnsureUnoptimizedCode(thread, function));
   if (!error.IsNull()) {