[builtins] Also migrate String.prototype.toLowerCase/toUpperCase to C++.

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/assert-scope.h"
@@ skipping 8843 matching lines @@
 
   bool ComputeArrayIndex(uint32_t* index);
 
   // Externalization.
   bool MakeExternal(v8::String::ExternalStringResource* resource);
   bool MakeExternal(v8::String::ExternalOneByteStringResource* resource);
 
   // Conversion.
   inline bool AsArrayIndex(uint32_t* index);
 
+  // Case conversion.
+  static MaybeHandle<String> ToLowerCase(Handle<String> string)
+      WARN_UNUSED_RESULT;
+  static MaybeHandle<String> ToUpperCase(Handle<String> string)
+      WARN_UNUSED_RESULT;
+
   // Trimming.
   enum TrimMode { kTrim, kTrimLeft, kTrimRight };
   static Handle<String> Trim(Handle<String> string, TrimMode mode);
 
   DECLARE_CAST(String)
 
   void PrintOn(FILE* out);
 
   // For use during stack traces.  Performs rudimentary sanity check.
   bool LooksValid();
@@ skipping 1916 matching lines @@
     }
     return value;
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #endif  // V8_OBJECTS_H_