In LayoutTestResult, change is_missing_* methods to accept explicit False.

This doesn't change any behavior in practice, since whenever is_missing_*
is present in a layout test dict, it's always true, as far as I know.

This change also changes did_run_as_expected.

So, this is just a minor tweak for correctness in case those fields are
ever explicitly given as False.

Review-Url: https://codereview.chromium.org/2326063003
Cr-Commit-Position: refs/heads/master@{#417967}

third_party/WebKit/Tools/Scripts/webkitpy/common/net/layouttestresults.py

@@ -51,23 +51,16 @@ class LayoutTestResult(object):
         return 'PASS' in self.actual_results()
 
     def did_run_as_expected(self):
-        # TODO(qyearsley): For correctness, this should be:
-        #     return not self._result_dict.get('is_unexpected', False)
-        # (Right now for expected results it's not added to the result dict
-        # but in theory it could be present.)
-        return 'is_unexpected' not in self._result_dict
+        return not self._result_dict.get('is_unexpected', False)
 
     def is_missing_image(self):
-        # TODO(qyearsley): Change this to:
-        #     self._result_dict.get('is_missing_image', False)
-        # The following method should likewise be changed.
-        return 'is_missing_image' in self._result_dict
+        return self._result_dict.get('is_missing_image', False)
 
     def is_missing_text(self):
-        return 'is_missing_text' in self._result_dict
+        return self._result_dict.get('is_missing_text', False)
 
     def is_missing_audio(self):
-        return 'is_missing_audio' in self._result_dict
+        return self._result_dict.get('is_missing_audio', False)
 
     def actual_results(self):
         return self._result_dict['actual']