Force subtree paint property updates on local border box changes

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

Index: third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
index a85f4ab2df70505ba856ed0b085898c24b1dfa0d..b94e8efb7ba77e2ac0b1533d9040376820a274e6 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintProperties.h
@@ -124,25 +124,49 @@ class CORE_EXPORT ObjectPaintProperties {
   const PropertyTreeStateWithOffset* localBorderBoxProperties() const {
     return m_localBorderBoxProperties.get();
   }
-  void updateLocalBorderBoxProperties(
-      LayoutPoint& paintOffset,
-      const TransformPaintPropertyNode* transform,
-      const ClipPaintPropertyNode* clip,
-      const EffectPaintPropertyNode* effect,
-      const ScrollPaintPropertyNode* scroll) {
-    if (m_localBorderBoxProperties) {
+  // True if local border box changes, false otherwise.
+  bool updateLocalBorderBoxProperties(LayoutPoint& paintOffset,
+                                      const TransformPaintPropertyNode* xform,
+                                      const ClipPaintPropertyNode* clip,
+                                      const EffectPaintPropertyNode* effect,
+                                      const ScrollPaintPropertyNode* scroll) {
+    if (!m_localBorderBoxProperties) {
+      m_localBorderBoxProperties = WTF::wrapUnique(
+          new ObjectPaintProperties::PropertyTreeStateWithOffset(
+              paintOffset, PropertyTreeState(xform, clip, effect, scroll)));
+      return true;
+    }
+    bool changed = false;
+    if (m_localBorderBoxProperties->paintOffset != paintOffset) {
       m_localBorderBoxProperties->paintOffset = paintOffset;

[Xianzhu, 2016/12/15 19:46:28]

What's the relationship between this check of paint offset change and the check
in PrePaintTreeWalk of paint offset change? Why doesn't the latter need paint
property update of subtree?

-      m_localBorderBoxProperties->propertyTreeState.setTransform(transform);
+      changed = true;
+    }
+    if (m_localBorderBoxProperties->propertyTreeState.transform() != xform) {
+      m_localBorderBoxProperties->propertyTreeState.setTransform(xform);
+      changed = true;
+    }
+    if (m_localBorderBoxProperties->propertyTreeState.clip() != clip) {
       m_localBorderBoxProperties->propertyTreeState.setClip(clip);
+      changed = true;
+    }
+    if (m_localBorderBoxProperties->propertyTreeState.effect() != effect) {
       m_localBorderBoxProperties->propertyTreeState.setEffect(effect);
+      changed = true;
+    }
+    if (m_localBorderBoxProperties->propertyTreeState.scroll() != scroll) {
       m_localBorderBoxProperties->propertyTreeState.setScroll(scroll);
-    } else {
-      m_localBorderBoxProperties = WTF::wrapUnique(
-          new ObjectPaintProperties::PropertyTreeStateWithOffset(
-              paintOffset, PropertyTreeState(transform, clip, effect, scroll)));
+      changed = true;
+    }
+    return changed;
+  }
+  // True if an existing property was deleted, false otherwise.
+  bool clearLocalBorderBoxProperties() {
+    if (m_localBorderBoxProperties) {
+      m_localBorderBoxProperties = nullptr;
+      return true;
     }
+    return false;
   }
-  void clearLocalBorderBoxProperties() { m_localBorderBoxProperties = nullptr; }
 
   // This is the complete set of property nodes and paint offset that can be
   // used to paint the contents of this object. It is similar to