Add full TurboFan support for accessing SeqString contents.

src/compiler/js-intrinsic-lowering.h

 // Copyright 2015 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_JS_INTRINSIC_LOWERING_H_
 #define V8_COMPILER_JS_INTRINSIC_LOWERING_H_
 
 #include "src/compiler/graph-reducer.h"
 #include "src/compiler/simplified-operator.h"
 
@@ skipping 22 matching lines @@
   Reduction ReduceDoubleLo(Node* node);
   Reduction ReduceHeapObjectGetMap(Node* node);
   Reduction ReduceIsInstanceType(Node* node, InstanceType instance_type);
   Reduction ReduceIsNonNegativeSmi(Node* node);
   Reduction ReduceIsSmi(Node* node);
   Reduction ReduceJSValueGetValue(Node* node);
   Reduction ReduceMapGetInstanceType(Node* node);
   Reduction ReduceMathClz32(Node* node);
   Reduction ReduceMathFloor(Node* node);
   Reduction ReduceMathSqrt(Node* node);
+  Reduction ReduceSeqStringGetChar(Node* node, String::Encoding encoding);
+  Reduction ReduceSeqStringSetChar(Node* node, String::Encoding encoding);
   Reduction ReduceStringGetLength(Node* node);
   Reduction ReduceValueOf(Node* node);
 
   Reduction Change(Node* node, const Operator* op);
   Reduction Change(Node* node, const Operator* op, Node* a, Node* b, Node* c);
 
   Graph* graph() const;
   JSGraph* jsgraph() const { return jsgraph_; }
   CommonOperatorBuilder* common() const;
   MachineOperatorBuilder* machine() const;
   SimplifiedOperatorBuilder* simplified() { return &simplified_; }
 
   JSGraph* jsgraph_;
   SimplifiedOperatorBuilder simplified_;
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_JS_INTRINSIC_LOWERING_H_