svg/repaint/image-with-clip-path.svg is flaky under guard malloc

svg/repaint/image-with-clip-path.svg is flaky under guard malloc
https://bugs.webkit.org/show_bug.cgi?id=77103

Reviewed by Zoltan Herczeg.

Fix image-with-clip-path.svg, to wait for the load of the resource, once href changes.
To do this properly, set externalResourcesRequired="true" which fires the onload event
if href changes, even if it was fired before already.

Added another testcase that only covers dynamic href changes, without using other resources.

* platform/mac/svg/repaint/image-href-change-expected.png: Added.
* platform/mac/svg/repaint/image-in-resource-href-change-expected.png: Removed.
* svg/repaint/image-href-change-expected.txt: Added.
* svg/repaint/image-href-change.svg: Added.
* svg/repaint/image-with-clip-path.svg: Fix test flakiness.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106103 268f45cc-cd09-0410-ab3c-d52691b4dbfc