[builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.

src/builtins.h

Index: src/builtins.h
diff --git a/src/builtins.h b/src/builtins.h
index 75761edfaeeb05e69ce06f073c558275791ac230..247ced67f7b83d9751e839556fec365420692abb 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -313,7 +313,9 @@ inline bool operator&(BuiltinExtraArguments lhs, BuiltinExtraArguments rhs) {
   V(MathRound, 2)                \
   V(MathSqrt, 2)                 \
   V(MathTrunc, 2)                \
-  V(ObjectHasOwnProperty, 2)
+  V(ObjectHasOwnProperty, 2)     \
+  V(StringPrototypeCharAt, 2)    \
+  V(StringPrototypeCharCodeAt, 2)
 
 // Define list of builtin handlers implemented in assembly.
 #define BUILTIN_LIST_H(V)                    \
@@ -629,6 +631,13 @@ class Builtins {
   static void Generate_ObjectHasOwnProperty(
       compiler::CodeStubAssembler* assembler);
 
+  // ES6 section 21.1.3.1 String.prototype.charAt ( pos )
+  static void Generate_StringPrototypeCharAt(
+      compiler::CodeStubAssembler* assembler);
+  // ES6 section 21.1.3.2 String.prototype.charCodeAt ( pos )
+  static void Generate_StringPrototypeCharCodeAt(
+      compiler::CodeStubAssembler* assembler);
+
   static void Generate_StringConstructor(MacroAssembler* masm);
   static void Generate_StringConstructor_ConstructStub(MacroAssembler* masm);
   static void Generate_OnStackReplacement(MacroAssembler* masm);