[PE] Stop dirtying compositing inputs on any layout for the root PaintLayer.

Instead, dirty them on particular PaintLayers only when their layout changed.

Bug: 410867
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Idf7664b869b1e7205e68adc075bcf828f279cffb
Reviewed-on: https://chromium-review.googlesource.com/1168142Reviewed-by: vmpstr <vmpstr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#582337}

third_party/blink/renderer/core/paint/compositing/paint_layer_compositor.cc

@@ -309,11 +309,6 @@ void PaintLayerCompositor::DidLayout() {
   // isScrollable method would return a different value.
   root_should_always_composite_dirty_ = true;
   EnableCompositingModeIfNeeded();
-
-  // FIXME: Rather than marking the entire LayoutView as dirty, we should
-  // track which Layers moved during layout and only dirty those
-  // specific Layers.
-  RootLayer()->SetNeedsCompositingInputsUpdate();
 }
 
 #if DCHECK_IS_ON()

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

@@ -325,6 +325,7 @@ void PaintLayer::UpdateLayerPositionsAfterLayout() {
 
 void PaintLayer::UpdateLayerPositionRecursive(
     UpdateLayerPositionBehavior behavior) {
+  LayoutPoint old_location = location_;
   switch (behavior) {
     case AllLayers:
       UpdateLayerPosition();
@@ -341,6 +342,9 @@ void PaintLayer::UpdateLayerPositionRecursive(
       NOTREACHED();
   }
 
+  if (location_ != old_location)
+    SetNeedsCompositingInputsUpdate();
+
   for (PaintLayer* child = FirstChild(); child; child = child->NextSibling())
     child->UpdateLayerPositionRecursive(behavior);
 }
@@ -925,6 +929,9 @@ bool PaintLayer::UpdateSize() {
   } else if (LayoutBox* box = GetLayoutBox()) {
     size_ = box->Size();
   }
+  if (old_size != size_)
+    SetNeedsCompositingInputsUpdate();
+
   return old_size != size_;
 }
 
@@ -3144,6 +3151,9 @@ void PaintLayer::StyleDidChange(StyleDifference diff,
       SetNeedsCompositingInputsUpdate();
   }
 
+  if (diff.NeedsLayout())
+    SetNeedsCompositingInputsUpdate();
+
   // A scroller that changes background color might become opaque or not
   // opaque, which in turn affects whether it can be composited on low-DPI
   // screens.

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

@@ -694,6 +694,7 @@ void PaintLayerScrollableArea::ContentsResized() {
   ScrollableArea::ContentsResized();
   // Need to update the bounds of the scroll property.
   GetLayoutBox()->SetNeedsPaintPropertyUpdate();
+  Layer()->SetNeedsCompositingInputsUpdate();
 }
 
 IntPoint PaintLayerScrollableArea::LastKnownMousePosition() const {

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

@@ -1805,6 +1805,9 @@ void FragmentPaintPropertyTreeBuilder::UpdateForObjectLocationAndSize(
     object_.GetMutableForPainting().SetMayNeedPaintInvalidation();
     fragment_data_.SetPaintOffset(context_.current.paint_offset);
     fragment_data_.InvalidateClipPathCache();
+
+    object_.GetFrameView()->SetNeedsIntersectionObservation(
+        LocalFrameView::kDesired);
   }
 
   if (paint_offset_translation)