[test] Search for use-strict in variant flags only.

Making test262's GetExpectedOutcomes independent from a command.
It will enable us to move this function to precompute phase.

Bug: v8:6917
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: Ibb59da29bd30f32427ba6230a22d7d0801954bf0
Reviewed-on: https://chromium-review.googlesource.com/828933Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michał Majewski <majeski@google.com>
Cr-Commit-Position: refs/heads/master@{#50127}

test/test262/testcfg.py

@@ -214,8 +214,7 @@ class TestSuite(testsuite.TestSuite):
 
   def GetExpectedOutcomes(self, test):
     outcomes = self.GetStatusFileOutcomes(test.name, test.variant)
-    if (statusfile.FAIL_SLOPPY in outcomes and
-        '--use-strict' not in test.cmd.args):
+    if (statusfile.FAIL_SLOPPY in outcomes and not test.uses_strict()):
       return [statusfile.FAIL]
     return super(TestSuite, self).GetExpectedOutcomes(test)
 
@@ -276,6 +275,9 @@ class TestCase(testcase.TestCase):
       return path
     return os.path.join(self.suite.testroot, filename)
 
+  def uses_strict(self):
+    return '--use-strict' in self.variant_flags
+
 
 def GetSuite(name, root):
   return TestSuite(name, root)