Avoid convertion to double when it is not needed.

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index d3baaa440cf7c49a64d1d3a5baeefa0eac4e1162..f7698eb189a34b6962da22812756e020af88bb96 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -857,9 +857,9 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_TypedArrayInitialize) {
   ASSERT(byte_length % elementSize == 0);
   size_t length = byte_length / elementSize;
 
-  Handle<Object> length_obj =
-      isolate->factory()->NewNumber(static_cast<double>(length));
+  Handle<Object> length_obj = isolate->factory()->NewNumberFromSize(length);
   holder->set_length(*length_obj);
+
   Handle<ExternalArray> elements =
       isolate->factory()->NewExternalArray(
           static_cast<int>(length), arrayType,