Run webgl_conformance_angle_tests on linux_optional_gpu_tests_rel.

content/test/gpu/generate_buildbot_json.py

 #!/usr/bin/env python
 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Script to generate chromium.gpu.json and chromium.gpu.fyi.json in
 the src/testing/buildbot directory. Maintaining these files by hand is
 too unwieldy.
 """
 
@@ skipping 1144 matching lines @@
     ],
     'target_name': 'webgl_conformance',
     'extra_browser_args': [
       '--use-angle=gl',
     ],
   },
   'webgl_conformance_angle_tests': {
     'tester_configs': [
       {
         'fyi_only': True,
-        'os_types': ['linux']
+        'os_types': ['linux'],
+        'run_on_optional': True,
       }
     ],
     'target_name': 'webgl_conformance',
     'extra_browser_args': [
       '--use-gl=angle',
     ],
   },
   'webgl2_conformance_tests': {
     'tester_configs': [
       {
@@ skipping 328 matching lines @@
     json.dump(tests, fp, indent=2, separators=(',', ': '), sort_keys=True)
     fp.write('\n')
 
 def main():
   generate_all_tests(FYI_WATERFALL, True)
   generate_all_tests(WATERFALL, False)
   return 0
 
 if __name__ == "__main__":
   sys.exit(main())