[turbofan] Introduce new Select operator to improve bounds checking.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index b4a62a1ecebf8cfc51be11481b74f7af918138c1..45004af18da1fe0c4b08cca837d9e234f013bd6d 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -535,6 +535,11 @@ Bounds Typer::Visitor::TypeExternalConstant(Node* node) {
 }
 
 
+Bounds Typer::Visitor::TypeSelect(Node* node) {
+  return Bounds::Either(Operand(node, 1), Operand(node, 2), zone());
+}
+
+
 Bounds Typer::Visitor::TypePhi(Node* node) {
   int arity = OperatorProperties::GetValueInputCount(node->op());
   Bounds bounds = Operand(node, 0);