Avoid convertion to double when it is not needed.

src/factory.h

Index: src/factory.h
diff --git a/src/factory.h b/src/factory.h
index 5e8970835b3d7dfc425496df4bc69bddaf42d804..233b3b01c824973f6376edccffa2d0aac131b89e 100644
--- a/src/factory.h
+++ b/src/factory.h
@@ -266,10 +266,12 @@ class Factory {
                                   PretenureFlag pretenure = NOT_TENURED);
   Handle<Object> NewNumberFromUint(uint32_t value,
                                   PretenureFlag pretenure = NOT_TENURED);
-
+  inline Handle<Object> NewNumberFromSize(size_t value,
+                                   PretenureFlag pretenure = NOT_TENURED);
   Handle<HeapNumber> NewHeapNumber(double value,
                                    PretenureFlag pretenure = NOT_TENURED);
 
+
   // These objects are used by the api to create env-independent data
   // structures in the heap.
   Handle<JSObject> NewNeanderObject();
@@ -539,6 +541,18 @@ class Factory {
 };
 
 
+Handle<Object> Factory::NewNumberFromSize(size_t value,
+                                          PretenureFlag pretenure) {
+  if (Smi::IsValid(static_cast<intptr_t>(value))) {
+    return Handle<Object>(Smi::FromIntptr(static_cast<intptr_t>(value)),
+                          isolate());
+  } else {
+    return NewNumber(static_cast<double>(value), pretenure);
+  }
+}
+
+
+
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_