GN: Initialize Tool::defined_from_ in the constructor

GN: Initialize Tool::defined_from_ in the constructor

set_defined_from() isn't called in some tests (e.g. those using TestWithScope),
thus calling defined_from() will only yield garbage, likely leading to a crash.

BUG=

Committed: https://crrev.com/fb7800730f213aba891c83df31b7183fc4cbcdc5
Cr-Commit-Position: refs/heads/master@{#423698}

[timn, 2016-10-06 21:16:53]

tim@rnc-ag.de changed reviewers:
+ brettw@chromium.org

[brettw, 2016-10-06 21:26:02]

awesome, thanks.

LGTM

[timn, 2016-10-06 21:28:48]

The CQ bit was checked by tim@rnc-ag.de

[commit-bot: I haz the power, 2016-10-06 21:29:37]

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, 2016-10-06 21:46:07]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-10-06 21:47:26]

Description was changed from

==========
GN: Initialize Tool::defined_from_ in the constructor

set_defined_from() isn't called in some tests (e.g. those using TestWithScope),
thus calling defined_from() will only yield garbage, likely leading to a crash.

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

to

==========
GN: Initialize Tool::defined_from_ in the constructor

set_defined_from() isn't called in some tests (e.g. those using TestWithScope),
thus calling defined_from() will only yield garbage, likely leading to a crash.

BUG=

Committed: https://crrev.com/fb7800730f213aba891c83df31b7183fc4cbcdc5
Cr-Commit-Position: refs/heads/master@{#423698}
==========

[commit-bot: I haz the power, 2016-10-06 21:47:27]

Patchset 1 (id:??) landed as
https://crrev.com/fb7800730f213aba891c83df31b7183fc4cbcdc5
Cr-Commit-Position: refs/heads/master@{#423698}