Introduce "optimized_out" oddball marker for compilers.

src/crankshaft/hydrogen-environment-liveness.cc

Index: src/crankshaft/hydrogen-environment-liveness.cc
diff --git a/src/crankshaft/hydrogen-environment-liveness.cc b/src/crankshaft/hydrogen-environment-liveness.cc
index ae0bd088376ada7be10d99ad394ea7e85c6c8a9c..7965a9432af7b02c6535cc8ffd68ccbc7b0bd1f2 100644
--- a/src/crankshaft/hydrogen-environment-liveness.cc
+++ b/src/crankshaft/hydrogen-environment-liveness.cc
@@ -37,9 +37,9 @@ void HEnvironmentLivenessAnalysisPhase::ZapEnvironmentSlot(
     int index, HSimulate* simulate) {
   int operand_index = simulate->ToOperandIndex(index);
   if (operand_index == -1) {
-    simulate->AddAssignedValue(index, graph()->GetConstantUndefined());
+    simulate->AddAssignedValue(index, graph()->GetConstantOptimizedOut());
   } else {
-    simulate->SetOperandAt(operand_index, graph()->GetConstantUndefined());
+    simulate->SetOperandAt(operand_index, graph()->GetConstantOptimizedOut());
   }
 }