[string] Add a fast path to String.p.replace

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 <memory>
 
@@ skipping 8185 matching lines @@
     virtual MaybeHandle<String> GetNamedCapture(Handle<String> name,
                                                 CaptureState* state) = 0;
 
     virtual ~Match() {}
   };
 
   // ES#sec-getsubstitution
   // GetSubstitution(matched, str, position, captures, replacement)
   // Expand the $-expressions in the string and return a new string with
   // the result.
+  // A {start_index} can be passed to specify where to start scanning the
+  // replacement string.
   MUST_USE_RESULT static MaybeHandle<String> GetSubstitution(
-      Isolate* isolate, Match* match, Handle<String> replacement);
+      Isolate* isolate, Match* match, Handle<String> replacement,
+      int start_index = 0);
 
   // String equality operations.
   inline bool Equals(String* other);
   inline static bool Equals(Handle<String> one, Handle<String> two);
   bool IsUtf8EqualTo(Vector<const char> str, bool allow_prefix_match = false);
 
   // Dispatches to Is{One,Two}ByteEqualTo.
   template <typename Char>
   bool IsEqualTo(Vector<const Char> str);
 
@@ skipping 2031 matching lines @@
   }
 };
 
 
 }  // NOLINT, false-positive due to second-order macros.
 }  // NOLINT, false-positive due to second-order macros.
 
 #include "src/objects/object-macros-undef.h"
 
 #endif  // V8_OBJECTS_H_