Bug 1546027 - Don't apply scroll anchor adjustments if we're restoring our scroll position. r=dholbert

Since scroll position restoration is absolute, and we'll lose it as soon as we
apply any adjustment or do any other sort of scrolling.

Differential Revision: https://phabricator.services.mozilla.com/D37941

--HG--
extra : moz-landing-system : lando

layout/generic/ScrollAnchorContainer.cpp

@@ -307,10 +307,14 @@ void ScrollAnchorContainer::Destroy() {
 }
 
 void ScrollAnchorContainer::ApplyAdjustments() {
-  if (!mAnchorNode || mAnchorNodeIsDirty) {
+  if (!mAnchorNode || mAnchorNodeIsDirty ||
+      mScrollFrame->HasPendingScrollRestoration()) {
     mSuppressAnchorAdjustment = false;
-    ANCHOR_LOG("Ignoring post-reflow (anchor=%p, dirty=%d, container=%p).\n",
+    ANCHOR_LOG(
-               mAnchorNode, mAnchorNodeIsDirty, this);
+        "Ignoring post-reflow (anchor=%p, dirty=%d, pendingRestoration=%d, "
+        "container=%p).\n",
+        mAnchorNode, mAnchorNodeIsDirty,
+        mScrollFrame->HasPendingScrollRestoration(), this);
     return;
   }
 

layout/generic/nsGfxScrollFrame.h

@@ -201,6 +201,10 @@ class ScrollFrameHelper : public nsIReflowCallback {
   void ScrollSnap(const nsPoint& aDestination,
                   ScrollMode aMode = ScrollMode::SmoothMsd);
 
+  bool HasPendingScrollRestoration() const {
+    return mRestorePos != nsPoint(-1, -1);
+  }
+
  protected:
   nsRect GetVisualScrollRange() const;