Bug 1490393 - Extract a helper method on StackingContextHelper to get the deferred transform matrix. r=mstange

Depends on D8108

Differential Revision: https://phabricator.services.mozilla.com/D8109

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

gfx/layers/wr/StackingContextHelper.cpp

@@ -95,5 +95,15 @@ StackingContextHelper::GetDeferredTransformItem() const
   return mDeferredTransformItem;
 }
 
+Maybe<gfx::Matrix4x4>
+StackingContextHelper::GetDeferredTransformMatrix() const
+{
+  if (mDeferredTransformItem) {
+    return Some((*mDeferredTransformItem)->GetTransform().GetMatrix());
+  } else {
+    return Nothing();
+  }
+}
+
 } // namespace layers
 } // namespace mozilla

gfx/layers/wr/StackingContextHelper.h

@@ -63,6 +63,7 @@ public:
   }
 
   const Maybe<nsDisplayTransform*>& GetDeferredTransformItem() const;
+  Maybe<gfx::Matrix4x4> GetDeferredTransformMatrix() const;
 
   bool AffectsClipPositioning() const { return mAffectsClipPositioning; }
   Maybe<wr::WrClipId> ReferenceFrameId() const { return mReferenceFrameId; }

gfx/layers/wr/WebRenderCommandBuilder.cpp

@@ -1511,14 +1511,14 @@ WebRenderCommandBuilder::CreateWebRenderCommandsFromDisplayList(nsDisplayList* a
           // stopAtAsr and |item|'s ASR in the ASR tree).
           mLayerScrollData.emplace_back();
           mLayerScrollData.back().Initialize(mManager->GetScrollData(), *deferred,
-              descendants, stopAtAsr, Some((*deferred)->GetTransform().GetMatrix()));
+              descendants, stopAtAsr, aSc.GetDeferredTransformMatrix());
         } else {
           // This is the "simple" case where we don't need to create two
           // WebRenderLayerScrollData items; we can just create one that also
           // holds the deferred transform matrix, if any.
           mLayerScrollData.emplace_back();
           mLayerScrollData.back().Initialize(mManager->GetScrollData(), item,
-              descendants, stopAtAsr, deferred ? Some((*deferred)->GetTransform().GetMatrix()) : Nothing());
+              descendants, stopAtAsr, aSc.GetDeferredTransformMatrix());
         }
       }
     }