Fix Crypto.getRandomValues to modify its argument, fix tests

tools/dom/templates/html/impl/impl_Crypto.darttemplate

+// Copyright (c) 2015, 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.
+
+part of $LIBRARYNAME;
+
+$(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
+
+  TypedData getRandomValues(TypedData array) {
+$if DART2JS
+    return _getRandomValues(array);
+$else
+    var random = _getRandomValues(array);
+    // The semantics of the operation are that it modifies the argument, but we
+    // have no way of making a Dart typed data created initially in Dart reference
+    // externalized storage. So we copy the values back from the returned copy.
+    // TODO(alanknight): Make this less ridiculously slow.
+    for (var i = 0; i < random.length; i++) {
+      array[i] = random[i];
+    }
+    return array;
+$endif
+  }
+
+$!MEMBERS
+}