[turbofan] Introduce DeadValue and DeadEffect operators.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index f92de92013249e981d62a5deec48ca9786117f61..5732cc238b20c2d0efe1ade8c2e0c3c7ee8b1463 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -742,6 +742,17 @@ Bounds Typer::Visitor::TypeFinish(Node* node) {
 }
 
 
+Bounds Typer::Visitor::TypeDeadValue(Node* node) {
+  return Bounds(Type::None(zone()), Type::Any(zone()));
+}
+
+
+Bounds Typer::Visitor::TypeDeadEffect(Node* node) {
+  UNREACHABLE();
+  return Bounds();
+}
+
+
 Bounds Typer::Visitor::TypeFrameState(Node* node) {
   // TODO(rossberg): Ideally FrameState wouldn't have a value output.
   return Bounds(Type::None(zone()), Type::Internal(zone()));