Run pkg-config for Udev only if use_udev==1

Run pkg-config for Udev only if use_udev==1

Some embedded platforms do not have udev support. The change will skip
running pkg-config if use_udev=0.

BUG=none

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=288770

[dnicoara, 2014-08-08 14:40:45]

PTAL

[brettw, 2014-08-11 16:37:11]

lgtm

[dnicoara, 2014-08-11 17:23:30]

The CQ bit was checked by dnicoara@chromium.org

[commit-bot: I haz the power, 2014-08-11 17:25:13]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/dnicoara@chromium.org/429723002/1

[commit-bot: I haz the power, 2014-08-11 19:49:36]

Change committed as 288770

[dnicoara, 2014-08-13 13:44:03]

A revert of this CL (patchset #1) has been created in
https://codereview.chromium.org/469763002/ by dnicoara@chromium.org.

The reason for reverting is: Breaks builds where use_udev==0 since certain
targets just assume udev and never check against use_udev.

Udev package should be wrapped in a use_udev confitional altogether and all the
locations using Udev should check against use_udev..

[brettw, 2014-08-13 20:37:48]

There's also //device/udev_linux. I don't really know what that is but a bunch
of targets link to it. It might be nice to move the udev pkg_config rule there.
The only reason this might be bad is it the udev config would be used by some
ChromeOS components that would see //build but not //device

[dnicoara, 2014-08-13 21:03:57]

On 2014/08/13 20:37:48, brettw wrote:
> There's also //device/udev_linux. I don't really know what that is but a bunch
> of targets link to it. It might be nice to move the udev pkg_config rule
there.
> The only reason this might be bad is it the udev config would be used by some
> ChromeOS components that would see //build but not //device

There are a couple different places that include the udev target directly. I
haven't followed all the dependencies but it gets hairy once you'd take into
account the unittests targets.

spang@ was nice and started updating all the places to perform a check against
use_udev==0  (https://codereview.chromium.org/467983002/)