Add explicit cast to avoid bug in analyzer.

pkg/collection_helpers/lib/typed_buffers.dart

Index: pkg/collection_helpers/lib/typed_buffers.dart
diff --git a/pkg/collection_helpers/lib/typed_buffers.dart b/pkg/collection_helpers/lib/typed_buffers.dart
index 06f83cf2d2d1c7833f5a617e03330d737816b21d..cad9a11ff4c669fca86460c5fc4b69385a294673 100644
--- a/pkg/collection_helpers/lib/typed_buffers.dart
+++ b/pkg/collection_helpers/lib/typed_buffers.dart
@@ -117,7 +117,9 @@ abstract class _TypedDataBuffer<E> extends ListBase<E> {
   void setRange(int start, int end, Iterable<E> source, [int skipCount = 0]) {
     if (end > _length) throw new RangeError.range(end, 0, _length);
     if (source is _TypedDataBuffer) {
-      _buffer.setRange(start, end, source._buffer, skipCount);
+      // Remove this cast when 15156 is fixed.

[floitsch, 2013/11/19 12:28:36]

TODO(15156): Remove this cast.

+      _TypedDataBuffer sourceBuffer = source;
+      _buffer.setRange(start, end, sourceBuffer._buffer, skipCount);
     } else {
       _buffer.setRange(start, end, source, skipCount);
     }