[EFL][WebGL] Enable webgl-background-color test.
https://bugs.webkit.org/show_bug.cgi?id=111428

Reviewed by Christophe Dumez.

This patch adds platform specific test expectation files for the
test and enables it for efl port.

* platform/efl/TestExpectations:
* platform/efl/compositing/webgl/webgl-background-color-expected.png: Added.
* platform/efl/compositing/webgl/webgl-background-color-expected.txt: Added.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@151350 268f45cc-cd09-0410-ab3c-d52691b4dbfc