Bug 1933423. Remove some unused fixed position display list code. r=jwatt

Only related in theme to this bug, but needed a place to put this cleanup.

Differential Revision: https://phabricator.services.mozilla.com/D230242

Author: tnikkel

layout/painting/nsDisplayList.cpp

@@ -2904,8 +2904,7 @@ nsDisplayBackgroundImage::nsDisplayBackgroundImage(
       mFillRect(aInitData.fillArea),
       mDestRect(aInitData.destArea),
       mLayer(aInitData.layer),
-      mIsRasterImage(aInitData.isRasterImage),
-      mShouldFixToViewport(aInitData.shouldFixToViewport) {
+      mIsRasterImage(aInitData.isRasterImage) {
   MOZ_COUNT_CTOR(nsDisplayBackgroundImage);
 #ifdef DEBUG
   if (mBackgroundStyle && mBackgroundStyle != mFrame->Style()) {
@@ -2916,7 +2915,7 @@ nsDisplayBackgroundImage::nsDisplayBackgroundImage(
 #endif
 
   mBounds = GetBoundsInternal(aInitData.builder, aFrameForBounds);
-  if (mShouldFixToViewport) {
+  if (aInitData.shouldFixToViewport) {
     // Expand the item's visible rect to cover the entire bounds, limited to the
     // viewport rect. This is necessary because the background's clip can move
     // asynchronously.

layout/painting/nsDisplayList.h

@@ -2534,14 +2534,6 @@ class nsDisplayItem {
     return Nothing();
   }
 
-  /**
-   * @return true if the contents of this item are rendered fixed relative
-   * to the nearest viewport.
-   */
-  virtual bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const {
-    return false;
-  }
-
   /**
    * Returns true if all layers that can be active should be forced to be
    * active. Requires setting the pref layers.force-active=true.
@@ -4195,9 +4187,6 @@ class nsDisplayBackgroundImage : public nsPaintedDisplayItem {
   void ComputeInvalidationRegion(nsDisplayListBuilder* aBuilder,
                                  const nsDisplayItemGeometry* aGeometry,
                                  nsRegion* aInvalidRegion) const override;
-  bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const override {
-    return mShouldFixToViewport;
-  }
 
   nsRect GetDestRect() const { return mDestRect; }
 
@@ -4249,8 +4238,6 @@ class nsDisplayBackgroundImage : public nsPaintedDisplayItem {
   nsRect mBounds;
   uint16_t mLayer;
   bool mIsRasterImage;
-  /* Whether the image should be treated as fixed to the viewport. */
-  bool mShouldFixToViewport;
 };
 
 /**
@@ -5660,10 +5647,6 @@ class nsDisplayFixedPosition : public nsDisplayOwnLayer {
                          mFrame->PresContext()->AppUnitsPerDevPixel());
   }
 
-  bool ShouldFixToViewport(nsDisplayListBuilder* aBuilder) const override {
-    return mIsFixedBackground;
-  }
-
   bool CreateWebRenderCommands(
       wr::DisplayListBuilder& aBuilder, wr::IpcResourceUpdateQueue& aResources,
       const StackingContextHelper& aSc,