Turn the NumberToStringStub into a hydrogen stub.

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 c3eac81671e4514f930579e3905c120f3e6aacc1..c76abcf001b96d250635c6afabdbaa0ab0266373 100644
--- a/src/x64/code-stubs-x64.h
+++ b/src/x64/code-stubs-x64.h
@@ -208,18 +208,6 @@ class StringCompareStub: public PlatformCodeStub {
 };
 
 
-class NumberToStringStub: public PlatformCodeStub {
- public:
-  NumberToStringStub() { }
-
- private:
-  Major MajorKey() { return NumberToString; }
-  int MinorKey() { return 0; }
-
-  void Generate(MacroAssembler* masm);
-};
-
-
 class NameDictionaryLookupStub: public PlatformCodeStub {
  public:
   enum LookupMode { POSITIVE_LOOKUP, NEGATIVE_LOOKUP };