[GTK] Layout Tests fast/dom/{Element,Range}/getClientRects.html are failing

[GTK] Layout Tests fast/dom/{Element,Range}/getClientRects.html are failing
https://bugs.webkit.org/show_bug.cgi?id=141700

Patch by Ms2ger <Ms2ger@igalia.com> on 2017-07-31
Reviewed by Sam Weinig.

Add gtk-specific expectations for getClientRects tests.

Since these expectations depend on text metrics, it is unsurprising that they
are platform-dependent.

* platform/gtk/TestExpectations:
* platform/gtk/fast/dom/Element/getClientRects-expected.txt: Added.
* platform/gtk/fast/dom/Range/getClientRects-expected.txt:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@220057 268f45cc-cd09-0410-ab3c-d52691b4dbfc