Fast path for string.replace that replaces a single character by a string.

src/runtime.h

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 179 matching lines @@
   /* JSON */ \
   F(ParseJson, 1, 1) \
   \
   /* Strings */ \
   F(StringCharCodeAt, 2, 1) \
   F(StringIndexOf, 3, 1) \
   F(StringLastIndexOf, 3, 1) \
   F(StringLocaleCompare, 2, 1) \
   F(SubString, 3, 1) \
   F(StringReplaceRegExpWithString, 4, 1) \
+  F(StringReplaceOneCharWithString, 3, 1) \
   F(StringMatch, 3, 1) \
   F(StringTrim, 3, 1) \
   F(StringToArray, 2, 1) \
   F(NewStringWrapper, 1, 1) \
   \
   /* Numbers */ \
   F(NumberToRadixString, 2, 1) \
   F(NumberToFixed, 2, 1) \
   F(NumberToExponential, 2, 1) \
   F(NumberToPrecision, 2, 1)
@@ skipping 412 matching lines @@
   // Alternatively, heap initialization can be completely restarted.
   MUST_USE_RESULT static MaybeObject* InitializeIntrinsicFunctionNames(
       Heap* heap, Object* dictionary);
 
   // Get the intrinsic function with the given name, which must be a symbol.
   static const Function* FunctionForSymbol(Handle<String> name);
 
   // Get the intrinsic function with the given FunctionId.
   static const Function* FunctionForId(FunctionId id);
 
+  static Handle<String> StringReplaceOneCharWithString(Isolate* isolate,
+                                                       Handle<String> subject,
+                                                       Handle<String> search,
+                                                       Handle<String> replace,
+                                                       bool* found);
+
   // General-purpose helper functions for runtime system.
   static int StringMatch(Isolate* isolate,
                          Handle<String> sub,
                          Handle<String> pat,
                          int index);
 
   static bool IsUpperCaseChar(RuntimeState* runtime_state, uint16_t ch);
 
   // TODO(1240886): Some of the following methods are *not* handle safe, but
   // accept handle arguments. This seems fragile.
@@ skipping 48 matching lines @@
 //---------------------------------------------------------------------------
 // Constants used by interface to runtime functions.
 
 class DeclareGlobalsEvalFlag:     public BitField<bool,         0, 1> {};
 class DeclareGlobalsNativeFlag:   public BitField<bool,         1, 1> {};
 class DeclareGlobalsLanguageMode: public BitField<LanguageMode, 2, 2> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_