Make stackmaps store their actual length.

runtime/vm/compiler.cc

Index: runtime/vm/compiler.cc
diff --git a/runtime/vm/compiler.cc b/runtime/vm/compiler.cc
index f785d282ac0eee18c964c4432113742909f8c47c..a4900a1fb354696c801009513ebc06184c256fc2 100644
--- a/runtime/vm/compiler.cc
+++ b/runtime/vm/compiler.cc
@@ -226,9 +226,6 @@ static bool CompileParsedFunctionHelper(
       const Function& function = parsed_function.function();
       const Code& code = Code::Handle(Code::FinalizeCode(function, &assembler));
       code.set_is_optimized(optimized);
-      if (optimized && use_ssa) {
-        code.set_spill_slot_count(graph_compiler.StackSize());
-      }
       graph_compiler.FinalizePcDescriptors(code);
       graph_compiler.FinalizeDeoptInfo(code);
       graph_compiler.FinalizeStackmaps(code);