Update DumpRenderTree2 to handle failing tests where no meaningful diff is available

Currently, DumpRenderTree2 asigns the following result codes
{PASS, FAIL_RESULT_DIFFERS, FAIL_NO_EXPECTED_RESULT, FAIL_TIMED_OUT,
FAIL_CRASHED}

This is not strictly correct, as a test may fail for any of three
reasons - crashing, timing out, or the the result not being as
expected. Therefore, it's possible for a test to fail even if the
result is as expected.

This patch updates AbstractResult to handle each of the three reasons
for failure separately. We then test all three to determine if the
test has passed.

This allows us to correctly report whether or not the result differs
from expected for a failing test.

Change-Id: I7adcfe72c4dd0bd3de2e1b868d9807be6eb5bddf