Bug 1508647 - Don't treat mSeparateLeaf as an output. r=aosmond

Differential Revision: https://phabricator.services.mozilla.com/D14473

--HG--
extra : moz-landing-system : lando

gfx/layers/wr/ClipManager.cpp

@@ -422,7 +422,6 @@ bool ClipManager::ItemClips::HasSameInputs(const ItemClips& aOther) {
 void ClipManager::ItemClips::CopyOutputsFrom(const ItemClips& aOther) {
   mScrollId = aOther.mScrollId;
   mClipChainId = aOther.mClipChainId;
-  mSeparateLeaf = aOther.mSeparateLeaf;
 }
 
 }  // namespace layers