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 5b91bb588887e821364ba63c5115867215c5eab3..a13cfcc0d881b56a4279e2839222911390373b75 100644
--- a/src/hydrogen-instructions.h
+++ b/src/hydrogen-instructions.h
@@ -5649,6 +5649,18 @@ 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);
   }