Introduce "optimized_out" oddball marker for compilers.

src/compiler/js-graph.cc

Index: src/compiler/js-graph.cc
diff --git a/src/compiler/js-graph.cc b/src/compiler/js-graph.cc
index e9387982878abc57434d67158c3b2dfa92fc717d..98ca7aa3c3f831dc36bb59e569ebc772447dedfc 100644
--- a/src/compiler/js-graph.cc
+++ b/src/compiler/js-graph.cc
@@ -29,6 +29,10 @@ Node* JSGraph::EmptyFixedArrayConstant() {
                 HeapConstant(factory()->empty_fixed_array()));
 }
 
+Node* JSGraph::OptimizedOutConstant() {
+  return CACHED(kOptimizedOutConstant,
+                HeapConstant(factory()->optimized_out()));
+}
 
 Node* JSGraph::UndefinedConstant() {
   return CACHED(kUndefinedConstant, HeapConstant(factory()->undefined_value()));