Add detail to 'invalid JSON' message in PRESUBMIT.py.

Add detail to 'invalid JSON' message in PRESUBMIT.py.

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=266019

[Thiemo Nagel, 2014-04-24 12:54:50]

Hi Jochen,

could you please have a look at this small improvement?

Thank you!
Thiemo

[jochen (gone - plz use gerrit), 2014-04-24 13:01:00]

lgtm

[Thiemo Nagel, 2014-04-24 13:05:52]

On 2014/04/24 13:01:00, jochen wrote:
> lgtm

Thank you!

[Thiemo Nagel, 2014-04-24 13:05:57]

The CQ bit was checked by tnagel@chromium.org

[commit-bot: I haz the power, 2014-04-24 13:48:33]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tnagel@chromium.org/255613002/1

[commit-bot: I haz the power, 2014-04-24 14:20:35]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-04-24 14:20:36]

Try jobs failed on following builders:
  tryserver.chromium on mac_chromium_compile_dbg

[Thiemo Nagel, 2014-04-24 16:35:20]

The CQ bit was checked by tnagel@chromium.org

[commit-bot: I haz the power, 2014-04-24 16:37:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/tnagel@chromium.org/255613002/1

[commit-bot: I haz the power, 2014-04-24 22:55:22]

Change committed as 266019