Skip gl surface init when headless; enable wm apptests.

mojo/tools/data/apptests

Index: mojo/tools/data/apptests
diff --git a/mojo/tools/data/apptests b/mojo/tools/data/apptests
index 0bcd7fda9243a0b42d1307f25a8d2099dac88bbe..a35da32f0c6725e90b9bf9fc910298d9e1b93fc2 100644
--- a/mojo/tools/data/apptests
+++ b/mojo/tools/data/apptests
@@ -44,9 +44,8 @@ tests = [
     "type": "gtest_isolated",
     "shell-args": ["--url-mappings=mojo:window_manager=mojo:test_window_manager"]
   },
-  # TODO(msw): Fix and enable window_manager_apptests: http://crbug.com/480040
-  #{
-  #  "test": "mojo:window_manager_apptests",
-  #  "shell-args": ["--use-test-config", "--use-headless-config"]
-  #},
+  {
+    "test": "mojo:window_manager_apptests",
+    "shell-args": ["--use-headless-config"]
+  },
 ]