[kernel] Don't output a -1 token position, it will crash observatory.

[kernel] Don't output a -1 token position, it will crash observatory.

Before this, for instance clicking on "dart:async" under "libraries"
would give a stacktrace and not show the source of "dart:async".
The cause was a "no position" (-1) mapping to column 0
(in what is supposed to be a 1-indexed world), thus becomming -1 in a
0-indexed world, being passed as the start index to indexOf yielding
an out-of-range exception.

BUG=
R=kustermann@google.com

Committed: https://github.com/dart-lang/sdk/commit/cac814a203cb1935bf1990fe5fd556344c2d85c4

[jensj, 2017-09-04 11:23:35]

jensj@google.com changed reviewers:
+ kustermann@google.com

[kustermann, 2017-09-04 11:28:40]

lgtm

[jensj, 2017-09-04 11:29:42]

Description was changed from

==========
[kernel] Don't output a -1 token position, it will crash observatory.

Before this, for instance clicking on "dart:async" under "libraries"
would give a stacktrace and not show the source of "dart:async".
The cause was a "no position" (-1) mapping to column 0
(in what is supposed to be a 1-indexed world), thus becomming -1 in a
0-indexed world, being passed as the start index to indexOf yielding
an out-of-range exception.

BUG=
==========

to

==========
[kernel] Don't output a -1 token position, it will crash observatory.

Before this, for instance clicking on "dart:async" under "libraries"
would give a stacktrace and not show the source of "dart:async".
The cause was a "no position" (-1) mapping to column 0
(in what is supposed to be a 1-indexed world), thus becomming -1 in a
0-indexed world, being passed as the start index to indexOf yielding
an out-of-range exception.

BUG=
R=kustermann@google.com

Committed:
https://github.com/dart-lang/sdk/commit/cac814a203cb1935bf1990fe5fd556344c2d85c4
==========

[jensj, 2017-09-04 11:29:43]

Committed patchset #1 (id:1) manually as
cac814a203cb1935bf1990fe5fd556344c2d85c4 (presubmit successful).