Speed-up 'new TypedArray(arrayLike)'.

src/typedarray.js

Index: src/typedarray.js
diff --git a/src/typedarray.js b/src/typedarray.js
index f9e732fa7f8f35bfd13598746c8a02f9af98b2ef..7bd16f670b4425b88319676a52374c480b5b2477 100644
--- a/src/typedarray.js
+++ b/src/typedarray.js
@@ -77,11 +77,10 @@ function CreateTypedArrayConstructor(name, elementSize, arrayId, constructor) {
   function ConstructByArrayLike(obj, arrayLike) {
     var length = arrayLike.length;
     var l =  ToPositiveInteger(length, "invalid_typed_array_length");
-    var byteLength = l * elementSize;
-    var buffer = new $ArrayBuffer(byteLength);
-    %TypedArrayInitialize(obj, arrayId, buffer, 0, byteLength);
-    for (var i = 0; i < l; i++) {
-      obj[i] = arrayLike[i];
+    if(!%TypedArrayInitializeFromArrayLike(obj, arrayId, arrayLike, l)) {
+      for (var i = 0; i < l; i++) {
+        obj[i] = arrayLike[i];
+      }
     }
   }