VR: Fix Linux unit test build

This target really needs to get into the CQ party.

BUG=
R=bshe

Change-Id: Ie276f66f7db7f09b019226c90a2ea0570c558a37
Reviewed-on: https://chromium-review.googlesource.com/684694Reviewed-by: Biao She <bshe@chromium.org>
Commit-Queue: Christopher Grant <cjgrant@chromium.org>
Cr-Commit-Position: refs/heads/master@{#504394}

chrome/browser/vr/BUILD.gn

@@ -197,6 +197,7 @@ test("vr_common_unittests") {
     "//skia",
     "//testing/gmock",
     "//testing/gtest",
+    "//ui/accessibility:ax_gen",
     "//ui/gfx:test_support",
     "//ui/gfx/geometry",
     "//ui/gl",