Add assists to move Flutter widgets up and down one level

Add assists to move Flutter widgets up and down one level.

Fixes:
https://github.com/flutter/flutter-intellij/issues/461

R=brianwilkerson@google.com

Committed: https://github.com/dart-lang/sdk/commit/b3ed30b8220b0a309572fe32f516c991cb8179ed

[messick, 2017-02-28 00:01:06]

Description was changed from

==========
Add assists to move Flutter widgets up and down one level
==========

to

==========
Add assists to move Flutter widgets up and down one level.

Fixes:
https://github.com/flutter/flutter-intellij/issues/461
==========

[messick, 2017-02-28 00:01:06]

messick@google.com changed reviewers:
+ brianwilkerson@google.com, devoncarew@google.com, scheglov@google.com

[messick, 2017-02-28 00:03:07]

Needs more tests, which will probably reveal problems, which I'll be glad to fix
after vacation.

This might be good enough for a scripted demo.

[Brian Wilkerson, 2017-02-28 00:14:36]

I agree it needs more tests, but still lgtm

https://codereview.chromium.org/2724473002/diff/1/pkg/analysis_server/lib/src...
File pkg/analysis_server/lib/src/services/correction/assist_internal.dart
(right):

https://codereview.chromium.org/2724473002/diff/1/pkg/analysis_server/lib/src...
pkg/analysis_server/lib/src/services/correction/assist_internal.dart:2424:
LineInfo lineInfo = new LineInfo.fromContent(currentSource);
There ought to be a better way to get the line info. Perhaps add a TODO to find
it.

[messick, 2017-02-28 01:03:55]

Description was changed from

==========
Add assists to move Flutter widgets up and down one level.

Fixes:
https://github.com/flutter/flutter-intellij/issues/461
==========

to

==========
Add assists to move Flutter widgets up and down one level.

Fixes:
https://github.com/flutter/flutter-intellij/issues/461

R=brianwilkerson@google.com

Committed:
https://github.com/dart-lang/sdk/commit/b3ed30b8220b0a309572fe32f516c991cb8179ed
==========

[messick, 2017-02-28 01:03:56]

Committed patchset #2 (id:20001) manually as
b3ed30b8220b0a309572fe32f516c991cb8179ed (presubmit successful).

[scheglov, 2017-02-28 01:07:28]

lgtm