Bug 1720995 - Don't apply the transform when painting a background-clip:text mask. r=miko

Differential Revision: https://phabricator.services.mozilla.com/D120688

layout/painting/nsDisplayList.cpp

@@ -8317,7 +8317,7 @@ void nsDisplayTransform::Paint(nsDisplayListBuilder* aBuilder, gfxContext* aCtx,
   }
 
   gfxContextMatrixAutoSaveRestore saveMatrix(aCtx);
-  Matrix4x4 trans = GetAccumulatedPreserved3DTransform(aBuilder);
+  Matrix4x4 trans = ShouldSkipTransform(aBuilder) ? Matrix4x4() : GetAccumulatedPreserved3DTransform(aBuilder);
   if (!IsFrameVisible(mFrame, trans)) {
     return;
   }

layout/reftests/backgrounds/background-clip-text-translate.html

@@ -0,0 +1,22 @@
+<meta charset="utf-8">
+
+<style>
+  body { overflow: hidden }
+  p {
+  margin: 1em 0;
+  padding: 1.4em;
+  font: 900 1.2em sans-serif;
+  position:absolute;
+  color: rgba(0,0,0,0);
+}
+
+.text {
+  background: red;
+  -webkit-background-clip: text;
+  background-clip: text;
+  transform: translate(-50%, -60%);
+  transform-origin: center;
+  left: 400px;
+  }
+</style>
+<p class="text">█</p>

layout/reftests/backgrounds/reftest.list

@@ -185,4 +185,5 @@ fuzzy-if(winWidget,0-102,0-2032) fuzzy-if(skiaContent,0-102,0-2811) fuzzy-if(web
 random-if(/^Windows\x20NT\x206\.1/.test(http.oscpu)) == background-clip-text-2.html background-clip-text-2-ref.html # Bug 1392106
 
 == background-clip-text-scale.html background-clip-text-scale-ref.html
+!= background-clip-text-translate.html about:blank
 != text-clip-and-stroke.html text-clip-and-no-stroke.html