[runtime] Add %ToString and %_ToString and remove the TO_STRING builtin.

src/compiler/js-generic-lowering.cc

Index: src/compiler/js-generic-lowering.cc
diff --git a/src/compiler/js-generic-lowering.cc b/src/compiler/js-generic-lowering.cc
index a5f9eeec764f70de8ee6833ef06726874f3df945..c845130bcd2a0af17eef1fdc85a057ab7c6c0ba8 100644
--- a/src/compiler/js-generic-lowering.cc
+++ b/src/compiler/js-generic-lowering.cc
@@ -296,7 +296,9 @@ void JSGenericLowering::LowerJSToNumber(Node* node) {
 
 
 void JSGenericLowering::LowerJSToString(Node* node) {
-  ReplaceWithBuiltinCall(node, Context::TO_STRING_BUILTIN_INDEX, 1);
+  CallDescriptor::Flags flags = AdjustFrameStatesForCall(node);
+  Callable callable = CodeFactory::ToString(isolate());
+  ReplaceWithStubCall(node, callable, flags);
 }