Bug 1453425 - Remove mScrollPosAtLastPaint from nsGfxScrollFrame. r=botond

This field appears to be only ever used as a local variable, and can be removed.

Differential Revision: https://phabricator.services.mozilla.com/D7126

--HG--
extra : rebase_source : 310057f703f4734ba9aef807100c5b5ff888da41
extra : histedit_source : 735d3f09bdb56d6eb386e2b5faffea1d769d97a1

layout/generic/nsGfxScrollFrame.cpp

@@ -2120,7 +2120,6 @@ ScrollFrameHelper::ScrollFrameHelper(nsContainerFrame* aOuter,
   , mLastSmoothScrollOrigin(nullptr)
   , mScrollGeneration(++sScrollGenerationCounter)
   , mDestination(0, 0)
-  , mScrollPosAtLastPaint(0, 0)
   , mRestorePos(-1, -1)
   , mLastPos(-1, -1)
   , mScrollPosForLayerPixelAlignment(-1, -1)
@@ -3395,10 +3394,9 @@ ScrollFrameHelper::BuildDisplayList(nsDisplayListBuilder*   aBuilder,
   mOuter->DisplayBorderBackgroundOutline(aBuilder, aLists);
 
   if (aBuilder->IsPaintingToWindow()) {
-    mScrollPosAtLastPaint = GetScrollPosition();
     if (IsMaybeScrollingActive()) {
       if (mScrollPosForLayerPixelAlignment == nsPoint(-1,-1)) {
-        mScrollPosForLayerPixelAlignment = mScrollPosAtLastPaint;
+        mScrollPosForLayerPixelAlignment = GetScrollPosition();
       }
     } else {
       mScrollPosForLayerPixelAlignment = nsPoint(-1,-1);

layout/generic/nsGfxScrollFrame.h

@@ -536,7 +536,6 @@ public:
   // just the current scroll position. ScrollBy will choose its
   // destination based on this value.
   nsPoint mDestination;
-  nsPoint mScrollPosAtLastPaint;
 
   // A goal position to try to scroll to as content loads. As long as mLastPos
   // matches the current logical scroll position, we try to scroll to mRestorePos