[PE] Don't invalidate compositing inputs on scroll.

An earlier patch (http://crrev.com/582337) regressed this.

Bug: 873883

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ie5fe1149ac1da2df7c1a59864339f5b5982527ff
Reviewed-on: https://chromium-review.googlesource.com/1183596
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585128}

third_party/blink/renderer/core/paint/paint_layer.cc

@@ -324,7 +324,8 @@ void PaintLayer::UpdateLayerPositionsAfterLayout() {
 }
 
 void PaintLayer::UpdateLayerPositionRecursive(
-    UpdateLayerPositionBehavior behavior) {
+    UpdateLayerPositionBehavior behavior,
+    bool dirty_compositing_if_needed) {
   LayoutPoint old_location = location_;
   switch (behavior) {
     case AllLayers:
@@ -342,7 +343,7 @@ void PaintLayer::UpdateLayerPositionRecursive(
       NOTREACHED();
   }
 
-  if (location_ != old_location)
+  if (dirty_compositing_if_needed && location_ != old_location)
     SetNeedsCompositingInputsUpdate();
 
   for (PaintLayer* child = FirstChild(); child; child = child->NextSibling())
@@ -424,12 +425,14 @@ void PaintLayer::UpdateLayerPositionsAfterOverflowScroll() {
     // offset is not included in clip rects. Therefore, we do not need to clear
     // them when that PaintLayer is scrolled. We also don't need to update layer
     // positions, because they also do not depend on the root's scroll offset.
-    if (GetScrollableArea()->HasStickyDescendants())
-      UpdateLayerPositionRecursive(OnlyStickyLayers);
+    if (GetScrollableArea()->HasStickyDescendants()) {
+      UpdateLayerPositionRecursive(OnlyStickyLayers,
+                                   /* dirty_compositing */ false);
+    }
     return;
   }
   ClearClipRects();
-  UpdateLayerPositionRecursive(AllLayers);
+  UpdateLayerPositionRecursive(AllLayers, /* dirty_compositing */ false);
 }
 
 void PaintLayer::UpdateTransformationMatrix() {

third_party/blink/renderer/core/paint/paint_layer.h

@@ -1103,7 +1103,8 @@ class CORE_EXPORT PaintLayer : public DisplayItemClient {
   bool HasOverflowControls() const;
 
   enum UpdateLayerPositionBehavior { AllLayers, OnlyStickyLayers };
-  void UpdateLayerPositionRecursive(UpdateLayerPositionBehavior = AllLayers);
+  void UpdateLayerPositionRecursive(UpdateLayerPositionBehavior = AllLayers,
+                                    bool dirty_compositing_if_needed = true);
 
   void SetNextSibling(PaintLayer* next) { next_ = next; }
   void SetPreviousSibling(PaintLayer* prev) { previous_ = prev; }