Early-out from the prepaint tree walk

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

Index: third_party/WebKit/Source/core/paint/FindPropertiesNeedingUpdate.h
diff --git a/third_party/WebKit/Source/core/paint/FindPropertiesNeedingUpdate.h b/third_party/WebKit/Source/core/paint/FindPropertiesNeedingUpdate.h
index fb3358b3aa74a4532ceb25d031c6e892b3e722f8..827c92de388f628589ca27bbc20ea09bd7b150ab 100644
--- a/third_party/WebKit/Source/core/paint/FindPropertiesNeedingUpdate.h
+++ b/third_party/WebKit/Source/core/paint/FindPropertiesNeedingUpdate.h
@@ -22,9 +22,13 @@ namespace blink {
 
 class FindFrameViewPropertiesNeedingUpdateScope {
  public:
-  FindFrameViewPropertiesNeedingUpdateScope(FrameView* frameView)
+  FindFrameViewPropertiesNeedingUpdateScope(
+      FrameView* frameView,
+      PaintPropertyTreeBuilderContext& context)
       : m_frameView(frameView),
-        m_neededPaintPropertyUpdate(frameView->needsPaintPropertyUpdate()) {
+        m_neededPaintPropertyUpdate(frameView->needsPaintPropertyUpdate()),
+        m_context(context),
+        m_hadForceSubtreeUpdate(context.forceSubtreeUpdate) {

[chrishtr, 2016/12/01 02:36:35]

Can you also use this field to check that forceSubtree was set to true due to
properties being set?

[pdr., 2016/12/01 09:35:35]

This class catches underinvalidation by checking that both property pointers and
property values do not change for objects not needing an update. If forceSubtree
were set to true while this checker is in scope, it would mean that property
pointers changed which this class should already check for.

     // No need to check when already marked as needing an update.
     if (m_neededPaintPropertyUpdate)
       return;
@@ -52,13 +56,16 @@ class FindFrameViewPropertiesNeedingUpdateScope {
     DCHECK_PTR_VAL_EQ(m_contentClip, m_frameView->contentClip());
     DCHECK_PTR_VAL_EQ(m_scrollTranslation, m_frameView->scrollTranslation());
     DCHECK_PTR_VAL_EQ(m_scroll, m_frameView->scroll());
-    // Restore original clean bit.
+    // Restore original clean bits.
     m_frameView->clearNeedsPaintPropertyUpdate();
+    m_context.forceSubtreeUpdate = m_hadForceSubtreeUpdate;
   }
 
  private:
   Persistent<FrameView> m_frameView;
   bool m_neededPaintPropertyUpdate;
+  PaintPropertyTreeBuilderContext& m_context;
+  bool m_hadForceSubtreeUpdate;
   RefPtr<TransformPaintPropertyNode> m_preTranslation;
   RefPtr<ClipPaintPropertyNode> m_contentClip;
   RefPtr<TransformPaintPropertyNode> m_scrollTranslation;
@@ -67,9 +74,13 @@ class FindFrameViewPropertiesNeedingUpdateScope {
 
 class FindObjectPropertiesNeedingUpdateScope {
  public:
-  FindObjectPropertiesNeedingUpdateScope(const LayoutObject& object)
+  FindObjectPropertiesNeedingUpdateScope(
+      const LayoutObject& object,
+      PaintPropertyTreeBuilderContext& context)
       : m_object(object),
-        m_neededPaintPropertyUpdate(object.needsPaintPropertyUpdate()) {
+        m_neededPaintPropertyUpdate(object.needsPaintPropertyUpdate()),
+        m_context(context),
+        m_hadForceSubtreeUpdate(context.forceSubtreeUpdate) {
     // No need to check when already marked as needing an update.
     if (m_neededPaintPropertyUpdate)
       return;
@@ -128,13 +139,16 @@ class FindObjectPropertiesNeedingUpdateScope {
     } else {
       DCHECK_EQ(!!m_properties, !!objectProperties);
     }
-    // Restore original clean bit.
+    // Restore original clean bits.
     const_cast<LayoutObject&>(m_object).clearNeedsPaintPropertyUpdate();
+    m_context.forceSubtreeUpdate = m_hadForceSubtreeUpdate;
   }
 
  private:
   const LayoutObject& m_object;
   bool m_neededPaintPropertyUpdate;
+  PaintPropertyTreeBuilderContext& m_context;
+  bool m_hadForceSubtreeUpdate;
   std::unique_ptr<const ObjectPaintProperties> m_properties;
 };