Improve srcset's layout tests
https://bugs.webkit.org/show_bug.cgi?id=120274

Moved srcset's tests to use js-test-pre, and output text with clear PASS/FAILED statements.
Added expected.txt files to the test directory, since there shouldn't be any platform variance in the results.
For some of the tests, added an equivalent 1x/2x test, to make sure the feature behaves on both DPRs.
Added preload tests on the "change-dynamically" tests, to make sure the 'src' resource is not loaded when it shouldn't.

Patch by Yoav Weiss <yoav@yoav.ws> on 2013-08-25
Reviewed by Andreas Kling.

* fast/hidpi/image-srcset-change-dynamically-from-js-1x-expected.txt: Added.
* fast/hidpi/image-srcset-change-dynamically-from-js-1x.html: Added.
* fast/hidpi/image-srcset-change-dynamically-from-js-2x-expected.txt: Added.
* fast/hidpi/image-srcset-change-dynamically-from-js-2x.html: Added.
* fast/hidpi/image-srcset-change-dynamically-from-js.html: Removed.
* fast/hidpi/image-srcset-data-src-expected.txt: Added.
* fast/hidpi/image-srcset-data-src.html:
* fast/hidpi/image-srcset-data-srcset-expected.txt: Added.
* fast/hidpi/image-srcset-data-srcset.html:
* fast/hidpi/image-srcset-invalid-inputs-correct-src-expected.txt: Added.
* fast/hidpi/image-srcset-invalid-inputs-correct-src.html:
* fast/hidpi/image-srcset-invalid-inputs-except-one-expected.txt: Added.
* fast/hidpi/image-srcset-invalid-inputs-except-one.html:
* fast/hidpi/image-srcset-remove-dynamically-from-js-expected.txt: Added.
* fast/hidpi/image-srcset-remove-dynamically-from-js.html:
* fast/hidpi/image-srcset-same-alternative-for-both-attributes-expected.txt: Added.
* fast/hidpi/image-srcset-same-alternative-for-both-attributes.html:
* fast/hidpi/image-srcset-simple-1x-expected.txt: Added.
* fast/hidpi/image-srcset-simple-1x.html: Added.
* fast/hidpi/image-srcset-simple-2x-expected.txt: Added.
* fast/hidpi/image-srcset-simple-2x.html: Added.
* fast/hidpi/image-srcset-simple.html: Removed.
* fast/hidpi/image-srcset-src-selection-1x-expected.txt: Added.
* fast/hidpi/image-srcset-src-selection-1x.html: Added.
* fast/hidpi/image-srcset-src-selection-2x-expected.txt: Added.
* fast/hidpi/image-srcset-src-selection-2x.html: Added.
* fast/hidpi/image-srcset-src-selection.html: Removed.
* fast/hidpi/image-srcset-viewport-modifiers-expected.txt: Added.
* fast/hidpi/image-srcset-viewport-modifiers.html:
* platform/mac/fast/hidpi/image-srcset-change-dynamically-from-js-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-data-src-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-data-srcset-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-invalid-inputs-correct-src-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-invalid-inputs-except-one-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-remove-dynamically-from-js-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-same-alternative-for-both-attributes-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-simple-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-src-selection-expected.txt: Removed.
* platform/mac/fast/hidpi/image-srcset-viewport-modifiers-expected.txt: Removed.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154582 268f45cc-cd09-0410-ab3c-d52691b4dbfc