Add tests for e?.v++, e?.v--, ++e?.v, and --e?.v.

Add tests for e?.v++, e?.v--, ++e?.v, and --e?.v.

The tests for e?.v++ and e?.v-- validate the spec text added in
58708e3 (as clarified by 1ab7736).

The tests for ++e?.v and --e?.v weren't mandated by any spec change,
but since these expressions weren't previously tested, it seemed
reasonable to add tests for them.

All tests pass under the current implementation of "?." in analyzer
and dart2js.

R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/76bbccf28f799efcbc2b6bd336b12a15d73844dd

[Paul Berry, 2015-06-17 17:18:33]

paulberry@google.com changed reviewers:
+ brianwilkerson@google.com

[Brian Wilkerson, 2015-06-17 17:30:31]

LGTM.

FYI, it looks like null-aware operators are going into the VM right now
(https://codereview.chromium.org/1180903002/).

[Paul Berry, 2015-06-17 18:08:43]

On 2015/06/17 17:30:31, Brian Wilkerson wrote:
> LGTM.
> 
> FYI, it looks like null-aware operators are going into the VM right now
> (https://codereview.chromium.org/1180903002/).

Thanks for the heads up.  I will coordinate with hausner@ before landing this.

[hausner, 2015-06-17 18:14:13]

hausner@google.com changed reviewers:
+ hausner@google.com

[hausner, 2015-06-17 18:14:14]

If you check in first, I'll make sure your new tests are passing in the VM.

[Paul Berry, 2015-06-17 18:14:53]

On 2015/06/17 18:14:14, hausner wrote:
> If you check in first, I'll make sure your new tests are passing in the VM.

Ok, thanks.  I will check in now.

[Paul Berry, 2015-06-17 18:17:44]

Committed patchset #1 (id:1) manually as
76bbccf28f799efcbc2b6bd336b12a15d73844dd (presubmit successful).