Pass --undefok to DM and nanobench for more graceful branch failure.

scripts/slave/recipes/skia/skia.expected/failed_dm.json

 [
   {
     "cmd": [
       "python",
       "-u",
       "[DEPOT_TOOLS]/gclient.py",
       "config",
       "--spec",
       "cache_dir = None\nsolutions = [{'deps_file': 'DEPS', 'managed': True, 'name': 'skia', 'url': 'https://skia.googlesource.com/skia.git'}]"
     ],
@@ skipping 315 matching lines @@
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  \"--dummy-flags\"@@@",
       "@@@STEP_LOG_LINE@json.output@]@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "catchsegv",
       "[SLAVE_BUILD]/skia/out/Debug/dm",
+      "--undefok",
       "--verbose",
       "--resourcePath",
       "[SLAVE_BUILD]/skia/resources",
       "--skps",
       "[SLAVE_BUILD]/playback/skps",
       "--images",
       "[SLAVE_BUILD]/images",
       "--writePath",
       "[SLAVE_BUILD]/dm",
       "--nameByHash",
@@ skipping 57 matching lines @@
       "@@@STEP_LOG_LINE@json.output@[@@@",
       "@@@STEP_LOG_LINE@json.output@  \"--dummy-flags\"@@@",
       "@@@STEP_LOG_LINE@json.output@]@@@",
       "@@@STEP_LOG_END@json.output@@@"
     ]
   },
   {
     "cmd": [
       "catchsegv",
       "[SLAVE_BUILD]/skia/out/Debug/nanobench",
+      "--undefok",
       "-i",
       "[SLAVE_BUILD]/skia/resources",
       "--skps",
       "[SLAVE_BUILD]/playback/skps",
       "--nogpu",
       "--dummy-flags"
     ],
     "name": "nanobench"
   },
   {
     "name": "$final_result",
     "reason": "Failed build steps: dm",
     "status_code": 1
   }
 ]