libgtk2ui should only add the cups config if use_cups is true

libgtk2ui should only add the cups config if use_cups is true

The cups gn config is defined inside a use_cups block,
therefore other targets should only try to add this config
inside another use_cups block.

Committed: https://crrev.com/e8eb9894ccb9b48af52b533397212f158244df91
Cr-Commit-Position: refs/heads/master@{#344268}

[Mostyn Bramley-Moore, 2015-08-19 12:10:30]

mostynb@opera.com changed reviewers:
+ brettw@chromium.org

[Mostyn Bramley-Moore, 2015-08-19 12:19:38]

@brettw: I have encountered a few issues in the GN build configuration like
this...  

I'm building some custom targets, which use the content api but nothing in the
chrome layer.  I have use_cups=false, which is fine for my target because cups
isn't used in anything in my dependency tree, but GN errors out when processing
a target in chrome/ that I will never build, eg in the libgtk2ui target.  I can
solve this problem by including the config inside a use_cups block, but if the
target requires use_cups then it seems odd to have to add if (use_cups) blocks
inside.  

Is there a policy or guideline for when to define targets inside conditional
blocks?

[brettw, 2015-08-19 17:01:15]

There's not really a good guideline. We just need to find the most clear thing
for particular cases.

LGTM

[Mostyn Bramley-Moore, 2015-08-19 17:06:48]

The CQ bit was checked by mostynb@opera.com

[commit-bot: I haz the power, 2015-08-19 17:07:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1296043003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1296043003/1

[commit-bot: I haz the power, 2015-08-19 17:55:53]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-19 17:56:44]

Patchset 1 (id:??) landed as
https://crrev.com/e8eb9894ccb9b48af52b533397212f158244df91
Cr-Commit-Position: refs/heads/master@{#344268}