Support StringCharCodeAt in hydrogen/lithium.

src/hydrogen.h

Index: src/hydrogen.h
diff --git a/src/hydrogen.h b/src/hydrogen.h
index 19f898381f02ab63c235ff45d329b5e7e78141a4..3524df949524a4835aea6a4ec4ab439b89e51f23 100644
--- a/src/hydrogen.h
+++ b/src/hydrogen.h
@@ -748,7 +748,10 @@ class HGraphBuilder: public AstVisitor {
   bool TryArgumentsAccess(Property* expr);
   bool TryCallApply(Call* expr);
   bool TryInline(Call* expr);
-  bool TryMathFunctionInline(Call* expr);
+  bool TryInlineBuiltinFunction(Call* expr,
+                                HValue* receiver,
+                                Handle<Map> receiver_map,
+                                CheckType check_type);
   void TraceInline(Handle<JSFunction> target, bool result);
 
   void HandleGlobalVariableAssignment(Variable* var,
@@ -772,6 +775,8 @@ class HGraphBuilder: public AstVisitor {
                                   ZoneMapList* types,
                                   Handle<String> name);
 
+  HStringCharCodeAt* BuildStringCharCodeAt(HValue* string,
+                                           HValue* index);
   HInstruction* BuildBinaryOperation(BinaryOperation* expr,
                                      HValue* left,
                                      HValue* right);