[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 294929a290189691014ea048fb1af2a669e22ea5..ea47f7e6f2a8e435d60da628235e5172add7fd90 100644
--- a/src/builtins.h
+++ b/src/builtins.h
@@ -310,7 +310,9 @@ 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)                    \
@@ -626,6 +628,13 @@ 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);