[turbofan] Introduce PlainPrimitiveToNumber.

src/compiler/js-graph.cc

Index: src/compiler/js-graph.cc
diff --git a/src/compiler/js-graph.cc b/src/compiler/js-graph.cc
index 4079f78cc0b86b877fb946a643b64b38fa77763c..e11543d5a37a41c84afce85b399734d6dc2100b4 100644
--- a/src/compiler/js-graph.cc
+++ b/src/compiler/js-graph.cc
@@ -24,6 +24,11 @@ Node* JSGraph::AllocateInOldSpaceStubConstant() {
                 HeapConstant(isolate()->builtins()->AllocateInOldSpace()));
 }
 
+Node* JSGraph::ToNumberBuiltinConstant() {
+  return CACHED(kToNumberBuiltinConstant,
+                HeapConstant(isolate()->builtins()->ToNumber()));
+}
+
 Node* JSGraph::CEntryStubConstant(int result_size) {
   if (result_size == 1) {
     return CACHED(kCEntryStubConstant,