Bug 1372603 - Remove the duplicated clip from WebRenderDisplayItemLayer. r=jrmuizel

Since part 1 of this patch set pushed the layer's local clip as part of
the code in ScrollingLayersHelper, it is no longer needed in the
WebRenderDisplayItemLayer (it is effectively duplicated).

MozReview-Commit-ID: F2HFsx3XI9M

--HG--
extra : rebase_source : 5dfcecb649376d6958760e4e95cd025d01f3124c

gfx/layers/wr/WebRenderDisplayItemLayer.cpp

@@ -40,29 +40,6 @@ WebRenderDisplayItemLayer::RenderLayer(wr::DisplayListBuilder& aBuilder,
 
   ScrollingLayersHelper scroller(this, aBuilder, aSc);
 
-  Maybe<WrImageMask> mask = BuildWrMaskLayer(aSc, nullptr);
-  WrImageMask* imageMask = mask.ptrOr(nullptr);
-
-  ParentLayerRect clip = GetLocalTransformTyped().TransformBounds(Bounds());
-
-  // As with WebRenderTextLayer, I'm not 100% sure this is correct, but I
-  // think it is. Because we don't push a stacking context for this layer,
-  // WR doesn't know about the transform on this layer. The display items
-  // that we push as part of this layer already take the transform into
-  // account. When we set the clip rect we also need to explicitly apply
-  // the transform to make sure it gets taken into account.
-  // In a sense this is the opposite of what WebRenderLayer::ClipRect() does,
-  // because there we remove the transform from the clip rect to bring it
-  // into the coordinate space of the local stacking context, but here we
-  // need to apply the transform to the bounds to take it into the coordinate
-  // space of the enclosing stacking context.
-  // The conversion from ParentLayerPixel to LayerPixel below is a result of
-  // changing the reference layer from "this layer" to the "the layer that
-  // created aSc".
-  LayerRect clipInParentLayerSpace = ViewAs<LayerPixel>(clip,
-      PixelCastJustification::MovingDownToChildren);
-  aBuilder.PushClip(aSc.ToRelativeWrRect(clipInParentLayerSpace), imageMask);
-
   if (mItem) {
     WrSize contentSize; // this won't actually be used by anything
     wr::DisplayListBuilder builder(WrBridge()->GetPipeline(), contentSize);
@@ -86,8 +63,6 @@ WebRenderDisplayItemLayer::RenderLayer(wr::DisplayListBuilder& aBuilder,
 
   aBuilder.PushBuiltDisplayList(Move(mBuiltDisplayList));
   WrBridge()->AddWebRenderParentCommands(mParentCommands);
-
-  aBuilder.PopClip();
 }
 
 Maybe<wr::ImageKey>