Fix two bugs with async stack traces.

Fix two bugs with async stack traces.

1. A crash when collecting an async stack trace with inlined frames on the stack.

2. A missing source position in an async stack trace.

Fixes #29080.

R=johnmccutchan@google.com

Committed: https://github.com/dart-lang/sdk/commit/ef7487a7a8b8604401cfafabe6bd2555b6847f17

[Florian Schneider, 2017-03-21 01:13:00]

fschneider@google.com changed reviewers:
+ rmacnak@google.com

[Cutch, 2017-03-21 13:59:16]

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

[Cutch, 2017-03-21 13:59:17]

lgtm

[Florian Schneider, 2017-03-21 16:31:17]

Description was changed from

==========
Fix two bugs with async stack traces.

1. A crash when collecting an async stack trace with inlined frames on the
stack.

2. A missing source position in an async stack trace.

Fixes #29080.
==========

to

==========
Fix two bugs with async stack traces.

1. A crash when collecting an async stack trace with inlined frames on the
stack.

2. A missing source position in an async stack trace.

Fixes #29080.

R=johnmccutchan@google.com

Committed:
https://github.com/dart-lang/sdk/commit/ef7487a7a8b8604401cfafabe6bd2555b6847f17
==========

[Florian Schneider, 2017-03-21 16:31:18]

Committed patchset #1 (id:1) manually as
ef7487a7a8b8604401cfafabe6bd2555b6847f17 (presubmit successful).