duration2_test.dart converted to a static-only test and skipped where appropriate for non-strong. error_stack_trace_test converted to a multitest and error_stack_trace1_test modified to use more modern catch convention for stack traces.
R=bkonyi@google.com, rnystrom@google.com
Review-Url: https://codereview.chromium.org/2987793002 .
Janice Collins