[SPv175] Reduce over-invalidation of repaint during style update on paint property change.

In SPv1 mode, LayoutObject::AdjustStyleDifference will cause subtree paint invalidation
(including PaintLayer repaint) on change of paint properties or z-index, but only
if there is no direct compositing reason for the object. The reason for the LayoutObject
paint invalidations was to cause raster invalidation as a side-effect. Painted
display list output of individual LayoutObjects does not change as a result of these
updates.

In SPv175 mode, we don't need to invalidate paint of individual LayoutObjects just
becaue of these changes, since raster invalidation happens via a new PaintChunk
mechanism. However, we still need to cause PaintLayer repaint if any paint property
tree nodes are added or removed, or z-index changes, to cause re-drawing of PaintChunks
with the correct paint properties and order.

There is already invalidation of PaintLayer repaint for paint property node change,
in PaintPropertyTreeBuilder::UpdateForSelf and ::UpdateForChildren (it was added
recently, after the code being removed in this CL was committed). Therefore we
only need to invalidate repaint for z-index change. Further, this is only needed
if the LayoutObject already had a PaintLayer, because z-index has no effect on
objects without a PaintLayer, and there is already invalidation happening on
PaintLayer addition or removal.

Tested by:

LayoutTests/paint/invalidation/compositing/chunk-reorder.html
svg/transforms/change-transform-to-none-shape.html

Bug:814711

Cq-Include-Trybots: master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Change-Id: I208b03b9e6b1a6635dab9585b8884ed0e2f8688d
Reviewed-on: https://chromium-review.googlesource.com/954352
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#541981}

third_party/WebKit/Source/core/layout/LayoutObject.cpp

@@ -2006,19 +2006,13 @@ void LayoutObject::SetStyle(scoped_refptr<ComputedStyle> style) {
 
   // Text nodes share style with their parents but the paint properties don't
   // apply to them, hence the !isText() check.
+  // In SPv175 mode, if property nodes are added or removed as a result of these
+  // style changes, PaintPropertyTreeBuilder will call SetNeedsRepaint
+  // to cause re-generation of PaintChunks.
   if (!IsText() && (diff.TransformChanged() || diff.OpacityChanged() ||
                     diff.ZIndexChanged() || diff.FilterChanged() ||
-                    diff.BackdropFilterChanged() || diff.CssClipChanged())) {
+                    diff.BackdropFilterChanged() || diff.CssClipChanged()))
     SetNeedsPaintPropertyUpdate();
-
-    // We don't need to invalidate paint of objects on SPv175 when only paint
-    // property or paint order change. Mark the painting layer needing repaint
-    // for changed paint property or paint order. Raster invalidation will be
-    // issued if needed during paint.
-    if (RuntimeEnabledFeatures::SlimmingPaintV175Enabled() &&
-        !ShouldDoFullPaintInvalidation())
-      ObjectPaintInvalidator(*this).SlowSetPaintingLayerNeedsRepaint();
-  }
 }
 
 void LayoutObject::StyleWillChange(StyleDifference diff,

third_party/WebKit/Source/core/paint/PaintLayer.cpp

@@ -3027,6 +3027,14 @@ void PaintLayer::StyleDidChange(StyleDifference diff,
 
   SetNeedsCompositingInputsUpdate();
   GetLayoutObject().SetNeedsPaintPropertyUpdate();
+
+  // We don't need to invalidate paint of objects on SPv175 when paint order
+  // changes. However, we do need to repaint the containing stacking context,
+  // in order to generate new paint chunks in the correct order. Raster
+  // invalidation will be issued if needed during paint.
+  if (RuntimeEnabledFeatures::SlimmingPaintV175Enabled() &&
+      diff.ZIndexChanged())
+    SetNeedsRepaint();
 }
 
 LayoutPoint PaintLayer::LocationInternal() const {

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.cpp

@@ -2264,7 +2264,8 @@ void ObjectPaintPropertyTreeBuilder::CreateFragmentContexts(
   }
 }
 
-void ObjectPaintPropertyTreeBuilder::UpdateFragments() {
+bool ObjectPaintPropertyTreeBuilder::UpdateFragments() {
+  bool had_paint_properties = object_.FirstFragment().PaintProperties();
   // Note: It is important to short-circuit on object_.StyleRef().ClipPath()
   // because NeedsClipPathClip() and NeedsEffect() requires the clip path
   // cache to be resolved, but the clip path cache invalidation must delayed
@@ -2305,6 +2306,8 @@ void ObjectPaintPropertyTreeBuilder::UpdateFragments() {
   }
 
   UpdateRepeatingPaintOffsetAdjustment();
+
+  return needs_paint_properties != had_paint_properties;
 }
 
 bool ObjectPaintPropertyTreeBuilder::ObjectTypeMightNeedPaintProperties()
@@ -2332,13 +2335,13 @@ void ObjectPaintPropertyTreeBuilder::UpdatePaintingLayer() {
 bool ObjectPaintPropertyTreeBuilder::UpdateForSelf() {
   UpdatePaintingLayer();
 
+  bool property_added_or_removed = false;
   if (ObjectTypeMightNeedPaintProperties())
-    UpdateFragments();
+    property_added_or_removed = UpdateFragments();
   else
     object_.GetMutableForPainting().FirstFragment().ClearNextFragment();
 
   bool property_changed = false;
-  bool property_added_or_removed = false;
   auto* fragment_data = &object_.GetMutableForPainting().FirstFragment();
   for (auto& fragment_context : context_.fragments) {
     FragmentPaintPropertyTreeBuilder builder(object_, context_,

third_party/WebKit/Source/core/paint/PaintPropertyTreeBuilder.h

@@ -198,7 +198,8 @@ class ObjectPaintPropertyTreeBuilder {
   ContextForFragment(const Optional<LayoutRect>& fragment_clip,
                      LayoutUnit logical_top_in_flow_thread) const;
   ALWAYS_INLINE void CreateFragmentContexts(bool needs_paint_properties);
-  ALWAYS_INLINE void UpdateFragments();
+  // Returns whether ObjectPaintProperties were allocated or deleted.
+  ALWAYS_INLINE bool UpdateFragments();
   ALWAYS_INLINE void UpdatePaintingLayer();
   ALWAYS_INLINE void UpdateRepeatingPaintOffsetAdjustment();
   ALWAYS_INLINE void UpdateRepeatingTableHeaderPaintOffsetAdjustment();