[turbofan] Added the RoundInt64ToFloat64 instruction to TurboFan.

src/compiler/typer.cc

Index: src/compiler/typer.cc
diff --git a/src/compiler/typer.cc b/src/compiler/typer.cc
index 6d54d20c5fd2da74ade307366bbe52d8cbef169d..51f4b628910ad264adc81fb8494e22830f88c8b3 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -2017,6 +2017,11 @@ Type* Typer::Visitor::TypeTruncateInt64ToInt32(Node* node) {
 }
 
 
+Type* Typer::Visitor::TypeRoundInt64ToFloat64(Node* node) {
+  return Type::Intersect(Type::PlainNumber(), Type::UntaggedFloat64(), zone());
+}
+
+
 Type* Typer::Visitor::TypeBitcastFloat32ToInt32(Node* node) {
   return Type::Number();
 }