Properly handle synchronous errors in Chain.capture. R=rnystrom@google.com BUG=19542 Review URL: https://codereview.chromium.org//344953002 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart/pkg/stack_trace@37520 260f80e4-7a28-3924-810f-c04153c831b5