Bug 1389139 - Add transforms for reflayer equivalents in the layers-free APZ world. r=jrmuizel

In normal gecko, RefLayer instances also have a transform, which needs
to be propagated to APZ in layers-free mode.

MozReview-Commit-ID: DaEyvpumG9F

--HG--
extra : rebase_source : 694dea8bdaa5a40cf52b2d3e99fdd4c335b6012c

layout/ipc/RenderFrameParent.cpp

@@ -390,9 +390,11 @@ nsDisplayRemote::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
 {
   MOZ_ASSERT(aManager->IsLayersFreeTransaction());
 
+  mOffset = mozilla::layout::GetContentRectLayerOffset(mFrame, aDisplayListBuilder);
+
   mozilla::LayoutDeviceRect visible = mozilla::LayoutDeviceRect::FromAppUnits(
       GetVisibleRect(), mFrame->PresContext()->AppUnitsPerDevPixel());
-  visible += mozilla::layout::GetContentRectLayerOffset(mFrame, aDisplayListBuilder);
+  visible += mOffset;
 
   aBuilder.PushIFrame(aSc.ToRelativeLayoutRect(visible),
       mozilla::wr::AsPipelineId(GetRemoteLayersId()));
@@ -406,6 +408,7 @@ nsDisplayRemote::UpdateScrollData(mozilla::layers::WebRenderScrollData* aData,
 {
   if (aLayerData) {
     aLayerData->SetReferentId(GetRemoteLayersId());
+    aLayerData->SetTransform(mozilla::gfx::Matrix4x4::Translation(mOffset.x, mOffset.y, 0.0));
   }
   return true;
 }

layout/ipc/RenderFrameParent.h

@@ -175,6 +175,7 @@ public:
 
 private:
   RenderFrameParent* mRemoteFrame;
+  mozilla::LayoutDeviceIntPoint mOffset;
   mozilla::layers::EventRegionsOverride mEventRegionsOverride;
 };