Fix crash in the flakiness dashboard server.

Tools/TestResultServer/model/datastorefile_test.py

Index: Tools/TestResultServer/model/datastorefile_test.py
diff --git a/Tools/TestResultServer/model/datastorefile_test.py b/Tools/TestResultServer/model/datastorefile_test.py
index 088cd94961651f7240db98a4c7077ab457987479..3ef32847aa36174a4556a86473abb7af188a82e7 100644
--- a/Tools/TestResultServer/model/datastorefile_test.py
+++ b/Tools/TestResultServer/model/datastorefile_test.py
@@ -57,6 +57,19 @@ class DataStoreFileTest(unittest.TestCase):
         self.test_file.delete_data()
         self.assertFalse(self.test_file.load_data())
 
+    def testLoadDataInvalidKey(self):
+        test_data = 'x' * datastorefile.MAX_ENTRY_LEN * 3
+
+        self.assertTrue(self.test_file.save_data(test_data))
+        self.assertEqual(test_data, self.test_file.data)
+
+        self.test_file.delete_data()
+        self.assertEqual('', self.test_file.load_data())
+
+    def testLoadDataNoKeys(self):
+        # This should never happen.
+        self.assertEqual(None, self.test_file.load_data())
+
     def testSaveData(self):
         self.assertFalse(self.test_file.save_data(None))