Add partial load test for JPEG image

Add partial load test for JPEG image
https://bugs.webkit.org/show_bug.cgi?id=98487

Reviewed by Adam Barth.

Partial load test: receive a partial number of image bytes and stall forever.  The partial
image should be decoded and drawn and the green <img> background should be visible.

* fast/images/resources/lenna.jpg: Added.
* http/tests/images/jpeg-partial-load-expected.png: Added.
* http/tests/images/jpeg-partial-load-expected.txt: Added.
* http/tests/images/jpeg-partial-load.html: Added.
* platform/chromium/http/tests/images/jpeg-partial-load-expected.png: Added.
* platform/mac/http/tests/images/jpeg-partial-load-expected.png: Added.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@130618 268f45cc-cd09-0410-ab3c-d52691b4dbfc