device: Add GN version of the device_unittests target.

Tested with the following command lines:

$ gn gen out_gn/Debug
$ ninja -C out_gn/Debug device_unittests
$ out_gn/Debug/device_unittests

BUG=None
TEST=see above
R=rockot@chromium.org

Review URL: https://codereview.chromium.org/912083003

Cr-Commit-Position: refs/heads/master@{#316058}

1 files changed, 1 insertions, 0 deletions

diff --git a/BUILD.gn b/BUILD.gn
index e47ef75..7dfa0b7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -261,6 +261,7 @@ group("root") {
   if (!is_android && !is_ios) {
     deps += [
       "//device/usb",
+      "//device:device_unittests",
       "//third_party/pdfium/samples",
     ]
   }