[Sheriff] Mark failing test for nacl port.

test/mjsunit/mjsunit.status

 # Copyright 2012 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 234 matching lines @@
   # Requires bigger stack size in the Genesis and if stack size is increased,
   # the test requires too much time to run.  However, the problem test covers
   # should be platform-independent.
   'regress/regress-1132': [SKIP],
 
   # Poor performance for NaCl V8 causes an assertion failure for this test.
   'regress/regress-165637': [SKIP],
 
   # Skip long running test that times out in debug mode and goes OOM on NaCl.
   'regress/regress-crbug-160010': [SKIP],
+
+  # Bug(v8:2978).
+  'lithium/MathExp': [PASS, FAIL],
 }],  # 'arch == nacl_ia32 or arch == nacl_x64'
 
 ##############################################################################
 ['deopt_fuzzer == True', {
 
   # Skip tests that are not suitable for deoptimization fuzzing.
   'assert-opt-and-deopt': [SKIP],
   'never-optimize': [SKIP],
   'regress/regress-2185-2': [SKIP],
   'harmony/object-observe': [SKIP],
   'readonly': [SKIP],
   'array-feedback': [SKIP],
 
   # Deopt every n garbage collections collides with deopt every n times.
   'regress/regress-2653': [SKIP],
 }],  # 'deopt_fuzzer == True'
 ]