Turn the NumberToStringStub into a hydrogen stub.

src/hydrogen-instructions.h

Index: src/hydrogen-instructions.h
diff --git a/src/hydrogen-instructions.h b/src/hydrogen-instructions.h
index 8cb2f591742aebec491d57d4ab9305b51cc1eeb4..a5cfe3b84d27fc2948b7715f6784b034eda1ee67 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5667,6 +5667,18 @@ class HObjectAccess V8_FINAL {
         kDouble, HeapNumber::kValueOffset, Representation::Double());
   }
 
+  static HObjectAccess ForHeapNumberValueLowestBits() {
+    return HObjectAccess(kDouble,
+                         HeapNumber::kValueOffset,
+                         Representation::Integer32());
+  }
+
+  static HObjectAccess ForHeapNumberValueHighestBits() {
+    return HObjectAccess(kDouble,
+                         HeapNumber::kValueOffset + kIntSize,
+                         Representation::Integer32());
+  }
+
   static HObjectAccess ForElementsPointer() {
     return HObjectAccess(kElementsPointer, JSObject::kElementsOffset);
   }