[compiler] Introduce StringEqualStub and StringNotEqualStub.

src/code-factory.h

Index: src/code-factory.h
diff --git a/src/code-factory.h b/src/code-factory.h
index 5f2426c1a547d52ab45878e92c37a3e731641590..3d1ae06b15bfb73bc1829a6f1230920d124a76d2 100644
--- a/src/code-factory.h
+++ b/src/code-factory.h
@@ -81,6 +81,8 @@ class CodeFactory final {
   static Callable StringAdd(Isolate* isolate, StringAddFlags flags,
                             PretenureFlag pretenure_flag);
   static Callable StringCompare(Isolate* isolate);
+  static Callable StringEqual(Isolate* isolate);
+  static Callable StringNotEqual(Isolate* isolate);
   static Callable SubString(Isolate* isolate);
 
   static Callable Typeof(Isolate* isolate);