From 3b2c342f3879705b0cc9919198b984f92aec5e62 Mon Sep 17 00:00:00 2001
From: wolfbeast <mcwerewolf@gmail.com>
Date: Fri, 2 Nov 2018 10:47:05 +0100
Subject: Make sure we remove our RefreshDriver observers in
 CompleteAsyncScroll.

Follow-up to fdbac095968bc952fec6a03765a7156940ae4733
---
 layout/generic/nsGfxScrollFrame.cpp | 11 +++++++++--
 layout/generic/nsGfxScrollFrame.h   |  3 +++
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/layout/generic/nsGfxScrollFrame.cpp b/layout/generic/nsGfxScrollFrame.cpp
index cfa366aa3..3ed3b0bb3 100644
--- a/layout/generic/nsGfxScrollFrame.cpp
+++ b/layout/generic/nsGfxScrollFrame.cpp
@@ -2152,8 +2152,7 @@ void
 ScrollFrameHelper::CompleteAsyncScroll(const nsRect &aRange, nsIAtom* aOrigin)
 {
   // Apply desired destination range since this is the last step of scrolling.
-  mAsyncSmoothMSDScroll = nullptr;
-  mAsyncScroll = nullptr;
+  RemoveObservers();
   nsWeakFrame weakFrame(mOuter);
   ScrollToImpl(mDestination, aRange, aOrigin);
   if (!weakFrame.IsAlive()) {
@@ -4588,11 +4587,19 @@ ScrollFrameHelper::Destroy()
     mScrollActivityTimer->Cancel();
     mScrollActivityTimer = nullptr;
   }
+  RemoveObservers();
+}
+
+void
+ScrollFrameHelper::RemoveObservers()
+{
   if (mAsyncScroll) {
     mAsyncScroll->RemoveObserver();
+    mAsyncScroll = nullptr;
   }
   if (mAsyncSmoothMSDScroll) {
     mAsyncSmoothMSDScroll->RemoveObserver();
+    mAsyncSmoothMSDScroll = nullptr;
   }
 }
 
diff --git a/layout/generic/nsGfxScrollFrame.h b/layout/generic/nsGfxScrollFrame.h
index f1ef44ae8..81bbb358f 100644
--- a/layout/generic/nsGfxScrollFrame.h
+++ b/layout/generic/nsGfxScrollFrame.h
@@ -638,6 +638,9 @@ protected:
   bool HasBgAttachmentLocal() const;
   uint8_t GetScrolledFrameDir() const;
 
+  // Removes any RefreshDriver observers we might have registered.
+  void RemoveObservers();
+
   static void EnsureFrameVisPrefsCached();
   static bool sFrameVisPrefsCached;
   // The number of scrollports wide/high to expand when tracking frame visibility.
-- 
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