The test layout/base/tests/chrome/test_chrome_over_plugin.xul fails due to plugin-container crashing on GTK3 with the following error: The program 'plugin-container' received an X Window System error. This probably reflects a bug in the program. The error was 'BadDrawable (invalid Pixmap or Window parameter)'. (Details: serial 280 error_code 9 request_code 14 minor_code 0) (Note to programmers: normally, X errors are reported asynchronously; that is, you will receive the error a while after causing it. To debug your program, run it with the --sync command line option to change this behavior. You can then get a meaningful backtrace from your debugger if you break on the gdk_x_error() function.)

This fixes bustage caused by an outdated (pre-GTK3) macro. Some tests in this suite still don't pass; I believe this to be unrelated and probably best tacked in a separate bug.

Try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=5af27cafdac4

Oops; GTK3 try patch wasn't building. Updated try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=cf810f3da26d