[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 6c80446ce921da7e1906cd4dfe3e74e2bca6ee61..749d862cb82e4eff4368a88ab34ef53ae9b92e80 100644
--- a/src/compiler/typer.cc
+++ b/src/compiler/typer.cc
@@ -1978,6 +1978,11 @@ Type* Typer::Visitor::TypeChangeInt32ToFloat64(Node* node) {
 }
 
 
+Type* Typer::Visitor::TypeChangeInt64ToFloat64(Node* node) {
+  return Type::Intersect(Type::Signed64(), Type::UntaggedFloat64(), zone());
+}
+
+
 Type* Typer::Visitor::TypeChangeInt32ToInt64(Node* node) {
   return Type::Internal();
 }