Introduce UdevDeviceGetSysattrValue

Introduce UdevDeviceGetSysattrValue, which is the same as
UdevDeviceGetPropertyValue but for sysattrs. Use this in places where
NULL is not an appropriate return value (such as assignment to
std::string).

Committed: https://crrev.com/df367dd86b9ad686d314f4664ae66674a1f700f0
Cr-Commit-Position: refs/heads/master@{#321043}

[Adam Goode, 2015-03-17 14:47:12]

agoode@chromium.org changed reviewers:
+ haven@chromium.org, rockot@chromium.org, thestig@chromium.org

[Lei Zhang, 2015-03-17 18:54:18]

lgtm

https://codereview.chromium.org/1018593002/diff/20001/device/udev_linux/udev.cc
File device/udev_linux/udev.cc (right):

https://codereview.chromium.org/1018593002/diff/20001/device/udev_linux/udev....
device/udev_linux/udev.cc:161:
device::udev_device_get_property_value(udev_device, key));
nit: no need for device:: within namespace device.

[Adam Goode, 2015-03-17 20:19:14]

https://codereview.chromium.org/1018593002/diff/20001/device/udev_linux/udev.cc
File device/udev_linux/udev.cc (right):

https://codereview.chromium.org/1018593002/diff/20001/device/udev_linux/udev....
device/udev_linux/udev.cc:161:
device::udev_device_get_property_value(udev_device, key));
On 2015/03/17 at 18:54:18, Lei Zhang wrote:
> nit: no need for device:: within namespace device.

Thanks, fixed.

[Ken Rockot(use gerrit already), 2015-03-17 20:21:34]

lgtm

[Adam Goode, 2015-03-18 00:50:34]

The CQ bit was checked by agoode@chromium.org

[Adam Goode, 2015-03-18 00:50:35]

The patchset sent to the CQ was uploaded after l-g-t-m from thestig@chromium.org
Link to the patchset: https://codereview.chromium.org/1018593002/#ps40001
(title: "Omit device:: in udev.cc for local functions")

[commit-bot: I haz the power, 2015-03-18 00:50:47]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1018593002/40001

[commit-bot: I haz the power, 2015-03-18 01:25:41]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-03-18 01:26:31]

Patchset 3 (id:??) landed as
https://crrev.com/df367dd86b9ad686d314f4664ae66674a1f700f0
Cr-Commit-Position: refs/heads/master@{#321043}