[turbofan] Introduce ObjectIsString operator.

src/compiler/opcodes.h

 // Copyright 2013 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_OPCODES_H_
 #define V8_COMPILER_OPCODES_H_
 
 #include <iosfwd>
 
 // Opcodes for control operators.
@@ skipping 196 matching lines @@
   V(Allocate)                      \
   V(LoadField)                     \
   V(LoadBuffer)                    \
   V(LoadElement)                   \
   V(StoreField)                    \
   V(StoreBuffer)                   \
   V(StoreElement)                  \
   V(ObjectIsNumber)                \
   V(ObjectIsReceiver)              \
   V(ObjectIsSmi)                   \
+  V(ObjectIsString)                \
   V(ObjectIsUndetectable)
 
 // Opcodes for Machine-level operators.
 #define MACHINE_COMPARE_BINOP_LIST(V) \
   V(Word32Equal)                      \
   V(Word64Equal)                      \
   V(Int32LessThan)                    \
   V(Int32LessThanOrEqual)             \
   V(Uint32LessThan)                   \
   V(Uint32LessThanOrEqual)            \
@@ skipping 201 matching lines @@
   }
 };
 
 std::ostream& operator<<(std::ostream&, IrOpcode::Value);
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_OPCODES_H_