[test] Make test duplication more robust

This makes test outcomes immutable. This has two benefits:
1) It's more robust. Using the |= operator by mistake
wouldn't lead to unwanted mutation.
2) It's faster as now the set reference can be copied again
when copying test cases. Test case copying happens an order
of magnitude more often than rules do apply.

BUG=v8:5238

Review-Url: https://codereview.chromium.org/2212333002
Cr-Commit-Position: refs/heads/master@{#38373}

tools/testrunner/local/testsuite.py

@@ -179,7 +179,7 @@ class TestSuite(object):
         used_rules.add((testname, variant))
         # Even for skipped tests, as the TestCase object stays around and
         # PrintReport() uses it.
-        t.outcomes |= rules[testname]
+        t.outcomes = t.outcomes | rules[testname]
         if statusfile.DoSkip(t.outcomes):
           continue  # Don't add skipped tests to |filtered|.
         for outcome in t.outcomes:
@@ -192,7 +192,7 @@ class TestSuite(object):
         assert rule[-1] == '*'
         if testname.startswith(rule[:-1]):
           used_rules.add((rule, variant))
-          t.outcomes |= wildcards[rule]
+          t.outcomes = t.outcomes | wildcards[rule]
           if statusfile.DoSkip(t.outcomes):
             skip = True
             break  # "for rule in wildcards"

tools/testrunner/objects/testcase.py

@@ -36,7 +36,7 @@ class TestCase(object):
     self.flags = flags or []  # list of strings, flags specific to this test
     self.variant = variant    # name of the used testing variant
     self.override_shell = override_shell
-    self.outcomes = set([])
+    self.outcomes = frozenset([])
     self.output = None
     self.id = None  # int, used to map result back to TestCase instance
     self.duration = None  # assigned during execution
@@ -45,7 +45,7 @@ class TestCase(object):
   def CopyAddingFlags(self, variant, flags):
     copy = TestCase(self.suite, self.path, variant, self.flags + flags,
                     self.override_shell)
-    copy.outcomes = set(self.outcomes)
+    copy.outcomes = self.outcomes
     return copy
 
   def PackTask(self):
@@ -63,7 +63,7 @@ class TestCase(object):
     """Creates a new TestCase object based on packed task data."""
     # For the order of the fields, refer to PackTask() above.
     test = TestCase(str(task[0]), task[1], task[2], task[3], task[4])
-    test.outcomes = set(task[5])
+    test.outcomes = frozenset(task[5])
     test.id = task[6]
     test.run = 1
     return test