Unalias effect nodes when determining whether it has opacity/distorsions

This patch unaliases effect nodes in two places in layout object:
- HasDistortingVisualEffects
- HasNonZeroEffectiveOpacity,

both of which navigate up the effect node chain and check properties.

R=chrishtr@chromium.org, pdr@chromium.org, wangxianzhu@chromium.org

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ib035679dff6822a7cc6127d6b7589e10a89e0cc3
Reviewed-on: https://chromium-review.googlesource.com/c/1265088Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Commit-Queue: vmpstr <vmpstr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597367}

third_party/blink/renderer/core/layout/layout_object.cc

@@ -1443,15 +1443,14 @@ bool LayoutObject::HasDistortingVisualEffects() const {
                                            .LocalBorderBoxProperties();
 
   // No filters, no blends, no opacity < 100%.
-  const EffectPaintPropertyNode* effects = paint_properties.Effect();
-  while (effects && !effects->IsRoot()) {
-    if (!effects->Filter().IsEmpty() ||
-        effects->GetColorFilter() != kColorFilterNone ||
-        effects->BlendMode() != SkBlendMode::kSrcOver ||
-        effects->Opacity() != 1.0) {
+  for (const auto* effect = SafeUnalias(paint_properties.Effect()); effect;
+       effect = SafeUnalias(effect->Parent())) {
+    if (!effect->Filter().IsEmpty() ||
+        effect->GetColorFilter() != kColorFilterNone ||
+        effect->BlendMode() != SkBlendMode::kSrcOver ||
+        effect->Opacity() != 1.0) {
       return true;
     }
-    effects = effects->Parent();
   }
 
   PropertyTreeState root_properties = GetDocument()
@@ -1477,11 +1476,10 @@ bool LayoutObject::HasNonZeroEffectiveOpacity() const {
                                            .FirstFragment()
                                            .LocalBorderBoxProperties();
 
-  const EffectPaintPropertyNode* effects = paint_properties.Effect();
-  while (effects && !effects->IsRoot()) {
-    if (effects->Opacity() == 0.0)
+  for (const auto* effect = SafeUnalias(paint_properties.Effect()); effect;
+       effect = SafeUnalias(effect->Parent())) {
+    if (effect->Opacity() == 0.0)
       return false;
-    effects = effects->Parent();
   }
   return true;
 }

third_party/blink/renderer/core/layout/layout_object_test.cc

@@ -790,6 +790,23 @@ TEST_F(LayoutObjectTest, HasDistortingVisualEffects) {
   ASSERT_TRUE(inner->GetLayoutObject()->HasDistortingVisualEffects());
 }
 
+TEST_F(LayoutObjectTest, DistortingVisualEffectsUnaliases) {
+  SetBodyInnerHTML(R"HTML(
+    <div style="opacity: 0.2;">
+      <div style="width: 100px height:100px; contain: paint">
+        <div id="child"
+             style="position: relative; width: 100px; height:100px;"></div>
+      </div>
+    </div>
+  )HTML");
+
+  const auto* child = GetDocument().getElementById("child");
+  const auto* object = child->GetLayoutObject();
+  // This should pass and not DCHECK if the nodes are unaliased correctly.
+  EXPECT_TRUE(object->HasDistortingVisualEffects());
+  EXPECT_TRUE(object->HasNonZeroEffectiveOpacity());
+}
+
 class LayoutObjectSimTest : public SimTest {
  public:
   bool DocumentHasTouchActionRegion(const EventHandlerRegistry& registry) {

third_party/blink/renderer/platform/graphics/paint/geometry_mapper.cc

@@ -9,11 +9,6 @@
 
 namespace blink {
 
-template <typename NodeType>
-const NodeType* SafeUnalias(const NodeType* node) {
-  return node ? node->Unalias() : nullptr;
-}
-
 const TransformationMatrix& GeometryMapper::SourceToDestinationProjection(
     const TransformPaintPropertyNode* source,
     const TransformPaintPropertyNode* destination) {

third_party/blink/renderer/platform/graphics/paint/paint_property_node.h

@@ -54,6 +54,11 @@ PLATFORM_EXPORT const TransformPaintPropertyNode& LowestCommonAncestorInternal(
     const TransformPaintPropertyNode&,
     const TransformPaintPropertyNode&);
 
+template <typename NodeType>
+const NodeType* SafeUnalias(const NodeType* node) {
+  return node ? node->Unalias() : nullptr;
+}
+
 template <typename NodeType>
 class PaintPropertyNode : public RefCounted<NodeType> {
  public: