Modify new-run-webkit-tests to return the percentage difference in image diffs where...

Modify new-run-webkit-tests to return the percentage difference in image diffs where possible.

https://bugs.webkit.org/show_bug.cgi?id=67253

Reviewed by Eric Seidel.

Tools:

Nearly all of the work in this was done by Simon Fraser; I'm
just repackaging it and cleaning it up a bit. This change
modifies port.diff_image() to return a tuple of (pass/fail,
%age), adds the value to the FailureImageHashMismatch, and
writes the value into the full_results.json files to be
displayed in the results page.

* Scripts/webkitpy/layout_tests/controllers/manager.py:
* Scripts/webkitpy/layout_tests/controllers/single_test_runner.py:
* Scripts/webkitpy/layout_tests/layout_package/test_result_writer.py:
* Scripts/webkitpy/layout_tests/models/test_failures.py:
* Scripts/webkitpy/layout_tests/port/base.py:
* Scripts/webkitpy/layout_tests/port/chromium.py:
* Scripts/webkitpy/layout_tests/port/chromium_unittest.py:
* Scripts/webkitpy/layout_tests/port/port_testcase.py:
* Scripts/webkitpy/layout_tests/port/test.py:
* Scripts/webkitpy/layout_tests/port/webkit.py:
* Scripts/webkitpy/layout_tests/run_webkit_tests_integrationtest.py:

LayoutTests:

* fast/harness/resources/results-test.js:
(mockExpectation):
(runDefaultSingleRowTest):
():
* fast/harness/results.html:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@96272 268f45cc-cd09-0410-ab3c-d52691b4dbfc