Move LayoutObject::m_previousPosition... into a global map in ObjectPaintInvalidator

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

Index: third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp
diff --git a/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp b/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp
index 5dac2b6796a97570578b3be9562eb3e3e32904dc..8da60adff69277ad1642617b892d8d33f8709110 100644
--- a/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp
+++ b/third_party/WebKit/Source/core/paint/ObjectPaintInvalidator.cpp
@@ -33,8 +33,20 @@ static void setPreviousSelectionVisualRect(const LayoutObject& object,
     selectionVisualRectMap().set(&object, rect);
 }
 
+typedef HashMap<const LayoutObject*, LayoutPoint> LocationInBackingMap;
+static LocationInBackingMap& locationInBackingMap() {
+  DEFINE_STATIC_LOCAL(LocationInBackingMap, map, ());
+  return map;
+}
+
 void ObjectPaintInvalidator::objectWillBeDestroyed(const LayoutObject& object) {
+  // TODO(wangxianzhu): Use the same mechanism as for locatinInBackingMap().
   selectionVisualRectMap().remove(&object);
+
+  DCHECK(object.hasPreviousLocationInBacking() ==
+         locationInBackingMap().contains(&object));
+  if (object.hasPreviousLocationInBacking())
+    locationInBackingMap().remove(&object);
 }
 
 // TODO(trchen): Use std::function<void, LayoutObject&> when available.
@@ -370,6 +382,29 @@ void ObjectPaintInvalidator::slowSetPaintingLayerNeedsRepaint() {
     paintingLayer->setNeedsRepaint();
 }
 
+LayoutPoint ObjectPaintInvalidator::previousLocationInBacking() const {
+  DCHECK(m_object.hasPreviousLocationInBacking() ==
+         locationInBackingMap().contains(&m_object));
+  return m_object.hasPreviousLocationInBacking()
+             ? locationInBackingMap().get(&m_object)
+             : m_object.previousVisualRect().location();
+}
+
+void ObjectPaintInvalidator::setPreviousLocationInBacking(
+    const LayoutPoint& location) {
+  DCHECK(m_object.hasPreviousLocationInBacking() ==
+         locationInBackingMap().contains(&m_object));
+  if (location == m_object.previousVisualRect().location()) {
+    if (m_object.hasPreviousLocationInBacking()) {
+      locationInBackingMap().remove(&m_object);
+      m_object.getMutableForPainting().setHasPreviousLocationInBacking(false);
+    }
+  } else {
+    locationInBackingMap().set(&m_object, location);
+    m_object.getMutableForPainting().setHasPreviousLocationInBacking(true);
+  }
+}
+
 void ObjectPaintInvalidatorWithContext::fullyInvalidatePaint(
     PaintInvalidationReason reason,
     const LayoutRect& oldVisualRect,