Revert of Optimize the pre-paint tree walk and ClipRects

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

Index: third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
diff --git a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
index 60b3765eb9acdeb320ecf1f18f69cff03ef69a41..3286c5641fe8d8d3d7be6e9171b7f25271eb7a63 100644
--- a/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
+++ b/third_party/WebKit/Source/core/paint/PrePaintTreeWalk.cpp
@@ -111,13 +111,31 @@
     context.ancestorOverflowPaintLayer = paintLayer;
 }
 
+// Returns whether |a| is an ancestor of or equal to |b|.
+static bool isAncestorOfOrEqualTo(const ClipPaintPropertyNode* a,
+                                  const ClipPaintPropertyNode* b) {
+  while (b && b != a) {
+    b = b->parent();
+  }
+  return b == a;
+}
+
 void PrePaintTreeWalk::computeClipRectForContext(
     const PaintPropertyTreeBuilderContext::ContainingBlockContext& context,
     const EffectPaintPropertyNode* effect,
     const PropertyTreeState& ancestorState,
     const LayoutPoint& ancestorPaintOffset,
+    bool& hasClip,
     FloatClipRect& clipRect) {
+  // Only return a non-infinite clip if clips differ, or the "ancestor" state is
+  // actually an ancestor clip. This ensures no accuracy issues due to
+  // transforms applied to infinite rects.
+  if (isAncestorOfOrEqualTo(context.clip, ancestorState.clip()))
+    clipRect = FloatClipRect();
+
+  hasClip = true;
   PropertyTreeState localState(context.transform, context.clip, effect);
+
   clipRect =
       m_geometryMapper.sourceToDestinationClipRect(localState, ancestorState);
   clipRect.moveBy(-FloatPoint(ancestorPaintOffset));
@@ -160,7 +178,8 @@
                              respectOverflowClip, LayoutSize());
 #endif
 
-  ClipRects clipRects;
+  bool hasClip = false;
+  RefPtr<ClipRects> clipRects = ClipRects::create();
   const LayoutPoint& ancestorPaintOffset =
       context.ancestorTransformedOrRootPaintLayer->layoutObject().paintOffset();
 
@@ -168,32 +187,36 @@
   const EffectPaintPropertyNode* effect =
       context.treeBuilderContext->currentEffect;
   computeClipRectForContext(context.treeBuilderContext->current, effect,
-                            ancestorState, ancestorPaintOffset, clipRect);
-  clipRects.setOverflowClipRect(clipRect);
-#ifdef CHECK_CLIP_RECTS
-  CHECK(clipRects->overflowClipRect() == oldClipRects.overflowClipRect())
+                            ancestorState, ancestorPaintOffset, hasClip,
+                            clipRect);
+  clipRects->setOverflowClipRect(clipRect);
+#ifdef CHECK_CLIP_RECTS
+  CHECK(!hasClip ||
+        clipRects->overflowClipRect() == oldClipRects.overflowClipRect())
       << "rect= " << clipRects->overflowClipRect().toString();
 #endif
 
   computeClipRectForContext(context.treeBuilderContext->fixedPosition, effect,
-                            ancestorState, ancestorPaintOffset, clipRect);
-  clipRects.setFixedClipRect(clipRect);
-#ifdef CHECK_CLIP_RECTS
-  CHECK(clipRects->fixedClipRect() == oldClipRects.fixedClipRect())
+                            ancestorState, ancestorPaintOffset, hasClip,
+                            clipRect);
+  clipRects->setFixedClipRect(clipRect);
+#ifdef CHECK_CLIP_RECTS
+  CHECK(hasClip || clipRects->fixedClipRect() == oldClipRects.fixedClipRect())
       << " fixed=" << clipRects->fixedClipRect().toString();
 #endif
 
   computeClipRectForContext(context.treeBuilderContext->absolutePosition,
-                            effect, ancestorState, ancestorPaintOffset,
+                            effect, ancestorState, ancestorPaintOffset, hasClip,
                             clipRect);
-  clipRects.setPosClipRect(clipRect);
-#ifdef CHECK_CLIP_RECTS
-  CHECK(clipRects->posClipRect() == oldClipRects.posClipRect())
+  clipRects->setPosClipRect(clipRect);
+#ifdef CHECK_CLIP_RECTS
+  CHECK(!hasClip || clipRects->posClipRect() == oldClipRects.posClipRect())
       << " abs=" << clipRects->posClipRect().toString();
 #endif
 
-  if (!paintLayer.hasPreviousPaintingClipRects() ||
-      clipRects != paintLayer.previousPaintingClipRects()) {
+  ClipRects* previousClipRects = paintLayer.previousPaintingClipRects();
+
+  if (!previousClipRects || *clipRects != *previousClipRects) {
     paintLayer.setNeedsRepaint();
     paintLayer.setPreviousPaintPhaseDescendantOutlinesEmpty(false);
     paintLayer.setPreviousPaintPhaseFloatEmpty(false);
@@ -204,7 +227,7 @@
         PaintInvalidatorContext::ForcedSubtreeInvalidationRectUpdate;
   }
 
-  paintLayer.setPreviousPaintingClipRects(clipRects);
+  paintLayer.setPreviousPaintingClipRects(*clipRects);
 }
 
 bool PrePaintTreeWalk::shouldEndWalkBefore(