[turbofan] Add Symbol feedback to Equal/StrictEqual.

src/type-hints.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_TYPE_HINTS_H_
 #define V8_TYPE_HINTS_H_
 
 #include "src/base/flags.h"
 #include "src/utils.h"
 
@@ skipping 17 matching lines @@
 std::ostream& operator<<(std::ostream&, BinaryOperationHint);
 
 // Type hints for an compare operation.
 enum class CompareOperationHint : uint8_t {
   kNone,
   kSignedSmall,
   kNumber,
   kNumberOrOddball,
   kInternalizedString,
   kString,
+  kSymbol,
   kReceiver,
   kAny
 };
 
 inline size_t hash_value(CompareOperationHint hint) {
   return static_cast<unsigned>(hint);
 }
 
 std::ostream& operator<<(std::ostream&, CompareOperationHint);
 
@@ skipping 38 matching lines @@
   STRING_ADD_CONVERT_LEFT = STRING_ADD_CHECK_LEFT | STRING_ADD_CONVERT,
   STRING_ADD_CONVERT_RIGHT = STRING_ADD_CHECK_RIGHT | STRING_ADD_CONVERT
 };
 
 std::ostream& operator<<(std::ostream& os, const StringAddFlags& flags);
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TYPE_HINTS_H_