Bug 903340. Make nsDisplayScrollInfoLayer::ShouldFlattenAway side-effect-free. r=tn

layout/base/nsDisplayList.cpp

@@ -3667,16 +3667,6 @@ nsDisplayScrollLayer::GetScrollLayerCount()
 #endif
 }
 
-intptr_t
-nsDisplayScrollLayer::RemoveScrollLayerCount()
-{
-  intptr_t result = GetScrollLayerCount();
-  FrameProperties props = mScrolledFrame->Properties();
-  props.Remove(nsIFrame::ScrollLayerCount());
-  return result;
-}
-
-
 nsDisplayScrollInfoLayer::nsDisplayScrollInfoLayer(
   nsDisplayListBuilder* aBuilder,
   nsIFrame* aScrolledFrame,
@@ -3688,12 +3678,12 @@ nsDisplayScrollInfoLayer::nsDisplayScrollInfoLayer(
 #endif
 }
 
-#ifdef NS_BUILD_REFCNT_LOGGING
 nsDisplayScrollInfoLayer::~nsDisplayScrollInfoLayer()
 {
+  FrameProperties props = mScrolledFrame->Properties();
+  props.Remove(nsIFrame::ScrollLayerCount());
   MOZ_COUNT_DTOR(nsDisplayScrollInfoLayer);
 }
-#endif
 
 LayerState
 nsDisplayScrollInfoLayer::GetLayerState(nsDisplayListBuilder* aBuilder,
@@ -3717,7 +3707,7 @@ nsDisplayScrollInfoLayer::ShouldFlattenAway(nsDisplayListBuilder* aBuilder)
   // one nsDisplayScrollLayer (with rendered content) or one
   // nsDisplayScrollInfoLayer (with only the metadata) should survive the
   // visibility computation.
-  return RemoveScrollLayerCount() == 1;
+  return GetScrollLayerCount() == 1;
 }
 
 nsDisplayZoom::nsDisplayZoom(nsDisplayListBuilder* aBuilder,

layout/base/nsDisplayList.h

@@ -2728,11 +2728,10 @@ public:
   // number does not include nsDisplayScrollInfoLayers. If this number is not 1
   // after merging, all the nsDisplayScrollLayers should flatten away.
   intptr_t GetScrollLayerCount();
-  intptr_t RemoveScrollLayerCount();
 
   virtual nsIFrame* GetScrolledFrame() { return mScrolledFrame; }
 
-private:
+protected:
   nsIFrame* mScrollFrame;
   nsIFrame* mScrolledFrame;
 };
@@ -2755,9 +2754,7 @@ public:
                            nsIFrame* aScrolledFrame, nsIFrame* aScrollFrame);
   NS_DISPLAY_DECL_NAME("ScrollInfoLayer", TYPE_SCROLL_INFO_LAYER)
 
-#ifdef NS_BUILD_REFCNT_LOGGING
   virtual ~nsDisplayScrollInfoLayer();
-#endif
 
   virtual LayerState GetLayerState(nsDisplayListBuilder* aBuilder,
                                    LayerManager* aManager,