[gtk] testuite Add translucent offscreen rendering test case

[Timm Bäder <baedert src gnome org>]

commit e0a7d283398990828fd6366e197a92f7b71ef4a3
Author: Timm Bäder <mail baedert org>
Date:   Sun Dec 2 16:15:17 2018 +0100

    testuite Add translucent offscreen rendering test case

 testsuite/gsk/gl/opacity_clip.gl.png | Bin 0 -> 543 bytes
 testsuite/gsk/gl/opacity_clip.node   | Bin 0 -> 293 bytes
 testsuite/gsk/meson.build            |   1 +
 3 files changed, 1 insertion(+)
---
diff --git a/testsuite/gsk/gl/opacity_clip.gl.png b/testsuite/gsk/gl/opacity_clip.gl.png
new file mode 100644
index 0000000000..95df90fc31
Binary files /dev/null and b/testsuite/gsk/gl/opacity_clip.gl.png differ
diff --git a/testsuite/gsk/gl/opacity_clip.node b/testsuite/gsk/gl/opacity_clip.node
new file mode 100644
index 0000000000..039a811cf9
Binary files /dev/null and b/testsuite/gsk/gl/opacity_clip.node differ
diff --git a/testsuite/gsk/meson.build b/testsuite/gsk/meson.build
index 5f18143f34..f2568a6710 100644
--- a/testsuite/gsk/meson.build
+++ b/testsuite/gsk/meson.build
@@ -52,6 +52,7 @@ gl_tests = [
   ['gradient simple',              'gradient_simple'],
   ['gradient transformed',         'gradient_transformed'],
   ['gradient clipped',             'gradient_clipped'],
+  ['offscreen opacity',            'opacity_clip'],
 ]
 
 foreach gl_test : gl_tests