Add ui_unittests to GN build.

Add ui_unittests to GN build.

Adds os_exchange_data_win_unittest.cc to Windows (it was incorrecly excluded before). Fixed a compilation error in that file.

Reland of 291154

R=sky@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=291483

[brettw, 2014-08-22 18:16:58]

This is a reland from https://codereview.chromium.org/496473003/

Previous change is in patch set 1.

It was incorrect to remove the exclusion of the chromeos unittests since it was
chromeos==0 or use_x11=1 and the new code didn't account for the x11=0 part of
the condition. The chromeos part of the condition is redundant due to the file
names, however.

[sky, 2014-08-22 19:30:51]

LGTM

[brettw, 2014-08-22 19:51:52]

Committed patchset #2 manually as 291483 (presubmit successful).