[turbofan] Add support for String.prototype.charCodeAt/charAt.

src/compiler/simplified-operator.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_SIMPLIFIED_OPERATOR_H_
 #define V8_COMPILER_SIMPLIFIED_OPERATOR_H_
 
 #include <iosfwd>
 
 #include "src/compiler/operator.h"
@@ skipping 233 matching lines @@
   const Operator* SpeculativeNumberLessThan(CompareOperationHints::Hint hint);
   const Operator* SpeculativeNumberLessThanOrEqual(
       CompareOperationHints::Hint hint);
   const Operator* SpeculativeNumberEqual(CompareOperationHints::Hint hint);
 
   const Operator* ReferenceEqual(Type* type);
 
   const Operator* StringEqual();
   const Operator* StringLessThan();
   const Operator* StringLessThanOrEqual();
+  const Operator* StringCharCodeAt();
   const Operator* StringFromCharCode();
 
   const Operator* PlainPrimitiveToNumber();
   const Operator* PlainPrimitiveToWord32();
   const Operator* PlainPrimitiveToFloat64();
 
   const Operator* ChangeTaggedSignedToInt32();
   const Operator* ChangeTaggedToInt32();
   const Operator* ChangeTaggedToUint32();
   const Operator* ChangeTaggedToFloat64();
@@ skipping 62 matching lines @@
   Zone* const zone_;
 
   DISALLOW_COPY_AND_ASSIGN(SimplifiedOperatorBuilder);
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_OPERATOR_H_