Unreviewed GTK gardening.

Provide the same custom expectations as all the other
platforms. This likely means that there is a bug in the code or
that the expected result is incorrect.

* platform/gtk/TestExpectations:
* platform/gtk/editing/pasteboard/5761530-1-expected.txt: Added.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142753 268f45cc-cd09-0410-ab3c-d52691b4dbfc