Get rid of the unused native code StringAddStub.

src/x64/code-stubs-x64.h

Index: src/x64/code-stubs-x64.h
diff --git a/src/x64/code-stubs-x64.h b/src/x64/code-stubs-x64.h
index fb05ff7f3c072ebe75e21e39e1e92b47136dcd93..c65307a74ecf594a740cbf4b5c73daa5f522e4c5 100644
--- a/src/x64/code-stubs-x64.h
+++ b/src/x64/code-stubs-x64.h
@@ -56,16 +56,6 @@ class StoreBufferOverflowStub: public PlatformCodeStub {
 
 class StringHelper : public AllStatic {
  public:
-  // Generate code for copying characters using a simple loop. This should only
-  // be used in places where the number of characters is small and the
-  // additional setup and checking in GenerateCopyCharactersREP adds too much
-  // overhead. Copying of overlapping regions is not supported.
-  static void GenerateCopyCharacters(MacroAssembler* masm,
-                                     Register dest,
-                                     Register src,
-                                     Register count,
-                                     bool ascii);
-
   // Generate code for copying characters using the rep movs instruction.
   // Copies rcx characters from rsi to rdi. Copying of overlapping regions is
   // not supported.
@@ -76,19 +66,6 @@ class StringHelper : public AllStatic {
                                         bool ascii);
 
 
-  // Probe the string table for a two character string. If the string is
-  // not found by probing a jump to the label not_found is performed. This jump
-  // does not guarantee that the string is not in the string table. If the
-  // string is found the code falls through with the string in register rax.
-  static void GenerateTwoCharacterStringTableProbe(MacroAssembler* masm,
-                                                   Register c1,
-                                                   Register c2,
-                                                   Register scratch1,
-                                                   Register scratch2,
-                                                   Register scratch3,
-                                                   Register scratch4,
-                                                   Label* not_found);
-
   // Generate string hash.
   static void GenerateHashInit(MacroAssembler* masm,
                                Register hash,
@@ -107,31 +84,6 @@ class StringHelper : public AllStatic {
 };
 
 
-class StringAddStub: public PlatformCodeStub {
- public:
-  explicit StringAddStub(StringAddFlags flags) : flags_(flags) {}
-
- private:
-  Major MajorKey() { return StringAdd; }
-  int MinorKey() { return flags_; }
-
-  void Generate(MacroAssembler* masm);
-
-  void GenerateConvertArgument(MacroAssembler* masm,
-                               int stack_offset,
-                               Register arg,
-                               Register scratch1,
-                               Register scratch2,
-                               Register scratch3,
-                               Label* slow);
-
-  void GenerateRegisterArgsPush(MacroAssembler* masm);
-  void GenerateRegisterArgsPop(MacroAssembler* masm, Register temp);
-
-  const StringAddFlags flags_;
-};
-
-
 class SubStringStub: public PlatformCodeStub {
  public:
   SubStringStub() {}