Revert of Move gn _run target generation into test().

ui/display/BUILD.gn

Index: ui/display/BUILD.gn
diff --git a/ui/display/BUILD.gn b/ui/display/BUILD.gn
index b8c760318babbea63d534cd95c37700e53f5f42e..6c6c181ae1ef4dc8d4d28e37195ca655423fc491 100644
--- a/ui/display/BUILD.gn
+++ b/ui/display/BUILD.gn
@@ -130,6 +130,15 @@
   }
 }
 
+# TODO(GYP): Delete this after we've converted everything to GN.
+# The _run targets exist only for compatibility w/ GYP.
+group("display_unittests_run") {
+  testonly = true
+  deps = [
+    ":display_unittests",
+  ]
+}
+
 # This test covers the ChromeOS "display" target as well as the cross-platform
 # //display/util target.
 test("display_unittests") {