Fix unaligned access to TypedData from native code.

tests/language/vm/unaligned_float_access_register_index_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+// VMOptions=--optimization_counter_threshold=10 --no-background_compilation
+
+import 'dart:typed_data';
+import 'package:expect/expect.dart';
+
+unalignedFloat32() {
+  var bytes = new ByteData(64);
+  for (var i = 0; i < 4; i++) {
+    bytes.setFloat32(i, 16.25);
+    Expect.equals(16.25, bytes.getFloat32(i));
+  }
+}
+
+unalignedFloat64() {
+  var bytes = new ByteData(64);
+  for (var i = 0; i < 8; i++) {
+    bytes.setFloat64(i, 16.25);
+    Expect.equals(16.25, bytes.getFloat64(i));
+  }
+}
+
+main() {
+  for (var i = 0; i < 20; i++) {
+    unalignedFloat32();
+    unalignedFloat64();
+  }
+}