new-run-webkit-tests: fix bugs in 'mock' drt implementation

new-run-webkit-tests: fix bugs in 'mock' drt implementation
https://bugs.webkit.org/show_bug.cgi?id=83341

Reviewed by Eric Seidel.

The current implementation crashed in some circumstances for
reference tests and files that were missing expected results.
This patch fixes those cases and adds more unit tests; it is a
precursor to adding unit tests each port that actually uses this
code, in order to get better coverage of the port/*
implementations.

* Scripts/webkitpy/layout_tests/port/mock_drt.py:
(parse_options):
(MockDRT.input_from_line):
(MockDRT.output_for_test):
(MockDRT.run_one_test):
(MockChromiumDRT.input_from_line):
(MockChromiumDRT.output_for_test):
(MockChromiumDRT.run_one_test):
* Scripts/webkitpy/layout_tests/port/mock_drt_unittest.py:
(MockDRTTest.make_input_output):
(MockDRTTest.expected_output):
(MockDRTTest):
(MockDRTTest.assertTest):
(MockDRTTest.test_missing_image):
(MockDRTTest.test_missing_text):
(MockDRTTest.test_reftest_match):
(MockDRTTest.test_reftest_mismatch):
(MockChromiumDRTTest.expected_output):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@113507 268f45cc-cd09-0410-ab3c-d52691b4dbfc