Add an --msan flag to run-tests.py.

tools/run-tests.py

Index: tools/run-tests.py
diff --git a/tools/run-tests.py b/tools/run-tests.py
index 66d1677aa11730a1176217e944312afc2cd82a06..dc73a4035fc364abbadb6ac23b5afeec3ee24ffd 100755
--- a/tools/run-tests.py
+++ b/tools/run-tests.py
@@ -257,6 +257,9 @@ def BuildOptions():
                     default="v8tests")
   result.add_option("--random-seed", default=0, dest="random_seed",
                     help="Default seed for initializing random generator")
+  result.add_option("--msan",
+                    help="Regard test expectations for MSAN",
+                    default=False, action="store_true")
   return result
 
 
@@ -509,6 +512,7 @@ def Execute(arch, mode, args, options, suites, workspace):
     "simulator": utils.UseSimulator(arch),
     "system": utils.GuessOS(),
     "tsan": options.tsan,
+    "msan": options.msan,
   }
   all_tests = []
   num_tests = 0