Implement creation of ByteData objects using the Dart API.

runtime/lib/typeddata.dart

Index: runtime/lib/typeddata.dart
===================================================================
--- runtime/lib/typeddata.dart	(revision 20330)
+++ runtime/lib/typeddata.dart	(working copy)
@@ -228,12 +228,12 @@
 patch class ByteData {
   /* patch */ factory ByteData(int length) {
     var list = new _Uint8Array(length);
-    return new _ByteDataView(list.buffer);
+    return new _ByteDataView(list.buffer, 0, length);
   }
 
   /* patch */ factory ByteData.transferable(int length) {

[vsm, 2013/03/21 18:35:27]

I don't see the transferable constructor declared in typeddata_base.dart.  Are
we really keeping this?

It will have no effect in dart2js (i.e., it will just forward to the primary
constructor), so it's really a question of whether Dartium or the VM still needs
this.

[siva, 2013/03/22 01:42:11]

I think Anton at one point wanted a way to create
External typed data objects in dart code so that it would
be easy to transfer them to other isolates in the same VM without copying. Not
sure if that is still applicable.

I didn't include them in the public interface as it was
not clear if it is needed or not. I am happy to remove it from here to and we
can add it back if we see a need.

On 2013/03/21 18:35:27, vsm wrote:

     var list = new _Uint8Array.transferable(length);
-    return new _ByteDataView(list.buffer);
+    return new _ByteDataView(list.buffer, 0, length);
   }
 
   /* patch */ factory ByteData.view(ByteBuffer buffer,