GN: update error message for invalid input_conversion.

GN: update error message for invalid input_conversion.

The current message is off-putting to read every time I get
input_conversion wrong.

BUG=

Committed: https://crrev.com/1c41ccaca266ec1272e5430a9fdc7145af043d20
Cr-Commit-Position: refs/heads/master@{#409008}

[mtklein_C, 2016-07-27 11:36:43]

mtklein@chromium.org changed reviewers:
+ brettw@chromium.org

[brettw, 2016-08-01 18:02:44]

lgtm

[mtklein_C, 2016-08-01 18:03:03]

The CQ bit was checked by mtklein@chromium.org

[commit-bot: I haz the power, 2016-08-01 18:03:46]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-08-01 18:46:48]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-08-01 18:48:56]

Description was changed from

==========
GN: update error message for invalid input_conversion.

The current message is off-putting to read every time I get
input_conversion wrong.

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

to

==========
GN: update error message for invalid input_conversion.

The current message is off-putting to read every time I get
input_conversion wrong.

BUG=

Committed: https://crrev.com/1c41ccaca266ec1272e5430a9fdc7145af043d20
Cr-Commit-Position: refs/heads/master@{#409008}
==========

[commit-bot: I haz the power, 2016-08-01 18:48:57]

Patchset 1 (id:??) landed as
https://crrev.com/1c41ccaca266ec1272e5430a9fdc7145af043d20
Cr-Commit-Position: refs/heads/master@{#409008}