Bug 1685009. Update the visual offset too when doing a paint skip transaction to keep it in sync with layout offset. r=botond

Differential Revision: https://phabricator.services.mozilla.com/D101149

gfx/layers/FrameMetrics.cpp

@@ -152,6 +152,24 @@ CSSPoint FrameMetrics::ApplyPureRelativeScrollUpdateFrom(
   return GetVisualScrollOffset() - origin;
 }
 
+void FrameMetrics::UpdatePendingScrollInfo(const ScrollPositionUpdate& aInfo) {
+  // We only get this "pending scroll info" for paint-skip transactions,
+  // but PureRelative position updates always trigger a full paint, so
+  // we should never enter this code with a PureRelative update type. For
+  // the other types, the destination field on the ScrollPositionUpdate will
+  // tell us the final layout scroll position on the main thread.
+  MOZ_ASSERT(aInfo.GetType() != ScrollUpdateType::PureRelative);
+
+  // In applying a main-thread scroll update, try to preserve the relative
+  // offset between the visual and layout viewports.
+  CSSPoint relativeOffset = GetVisualScrollOffset() - GetLayoutScrollOffset();
+  MOZ_ASSERT(IsRootContent() || relativeOffset == CSSPoint());
+
+  SetLayoutScrollOffset(aInfo.GetDestination());
+  ClampAndSetVisualScrollOffset(aInfo.GetDestination() + relativeOffset);
+  mScrollGeneration = aInfo.GetGeneration();
+}
+
 ScrollSnapInfo::ScrollSnapInfo()
     : mScrollSnapStrictnessX(StyleScrollSnapStrictness::None),
       mScrollSnapStrictnessY(StyleScrollSnapStrictness::None) {}

gfx/layers/FrameMetrics.h

@@ -266,16 +266,7 @@ struct FrameMetrics {
   CSSPoint ApplyPureRelativeScrollUpdateFrom(
       const ScrollPositionUpdate& aUpdate);
 
-  void UpdatePendingScrollInfo(const ScrollPositionUpdate& aInfo) {
-    // We only get this "pending scroll info" for paint-skip transactions,
-    // but PureRelative position updates always trigger a full paint, so
-    // we should never enter this code with a PureRelative update type. For
-    // the other types, the destination field on the ScrollPositionUpdate will
-    // tell us the final layout scroll position on the main thread.
-    MOZ_ASSERT(aInfo.GetType() != ScrollUpdateType::PureRelative);
-    SetLayoutScrollOffset(aInfo.GetDestination());
-    mScrollGeneration = aInfo.GetGeneration();
-  }
+  void UpdatePendingScrollInfo(const ScrollPositionUpdate& aInfo);
 
  public:
   void SetPresShellResolution(float aPresShellResolution) {

gfx/tests/crashtests/1685009-1.html

@@ -0,0 +1,12 @@
+<script>
+window.requestIdleCallback(() => {
+  window.close();
+})
+window.onload = () => {
+  a.value = "J."
+  b.submit()
+  window.requestAnimationFrame(() => { a.setRangeText("foo") })
+}
+</script>
+<textarea id="a" style="max-width: 0"></textarea>
+<form id="b" target="a">

gfx/tests/crashtests/crashtests.list

@@ -200,4 +200,4 @@ skip-if(!webrender||AddressSanitizer) load 1652750-deep-scene-stack.html
 load 1651882.html
 skip-if(!webrender) load 1678938-1.html
 load 1679477-1.html
-
+skip-if(Android) pref(dom.disable_open_during_load,false) load 1685009-1.html