Issue 21291. Fix for selecting navigation region.

R=brianwilkerson@google.com
BUG= https://code.google.com/p/dart/issues/detail?id=21291

Review URL: https://codereview.chromium.org//649123002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41065 260f80e4-7a28-3924-810f-c04153c831b5
Wait for field values with timeout in case of VM / Debugger problems.

This code is called from UI, so we should not await without a timeout.

R=devoncarew@google.com
BUG=

Review URL: https://codereview.chromium.org//644203002

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@41066 260f80e4-7a28-3924-810f-c04153c831b5