Don't include scroll offset in offsetFromLayoutObject for scrolling contents layers.

third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
index 9081857db32c0caf9d08620a6d0a46f5ebc4eb72..cd3587ad63c36c9c01f3a8c43e808791cc8e3b93 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBoxModelObject.cpp
@@ -412,6 +412,11 @@ void LayoutBoxModelObject::invalidateTreeIfNeeded(const PaintInvalidationState&
     invalidatePaintOfSubtreesIfNeeded(newPaintInvalidationState);
 }
 
+static bool compositedScrollsWithRespectTo(const LayoutObject* layoutObject, const LayoutBoxModelObject& paintInvalidationContainer)

[wkorman, 2016/05/31 18:34:15]

If layoutObject is never null can use const &?

[chrishtr, 2016/05/31 18:51:54]

It can be null, due to the default parameter of
invalidateDisplayItemClientOnBacking.

+{
+    return paintInvalidationContainer.usesCompositedScrolling() && layoutObject != &paintInvalidationContainer;
+}
+
 void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRect& r, PaintInvalidationReason invalidationReason, const LayoutObject& object) const
 {
     // TODO(wangxianzhu): Enable the following assert after paint invalidation for spv2 is ready.
@@ -428,12 +433,15 @@ void LayoutBoxModelObject::setBackingNeedsPaintInvalidationInRect(const LayoutRe
             // Note: the subpixel accumulation of layer() does not need to be added here. It is already taken into account.
             squashingLayer->setNeedsDisplayInRect(enclosingIntRect(paintInvalidationRect), invalidationReason, object);
         }
+    } else if (compositedScrollsWithRespectTo(&object, *this)) {
+        layer()->compositedLayerMapping()->setScrollingContentsNeedDisplayInRect(r, invalidationReason, object);
     } else {
+        // TODO(chrishtr): we should be able to skip scrolling content layers in this case.
         layer()->compositedLayerMapping()->setContentsNeedDisplayInRect(r, invalidationReason, object);
     }
 }
 
-void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClient& displayItemClient, PaintInvalidationReason invalidationReason) const
+void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayItemClient& displayItemClient, PaintInvalidationReason invalidationReason, const LayoutObject* layoutObject) const
 {
     displayItemClient.setDisplayItemsUncached();
 
@@ -448,7 +456,10 @@ void LayoutBoxModelObject::invalidateDisplayItemClientOnBacking(const DisplayIte
         if (GraphicsLayer* squashingLayer = layer()->groupedMapping()->squashingLayer())
             squashingLayer->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
     } else if (CompositedLayerMapping* compositedLayerMapping = layer()->compositedLayerMapping()) {
-        compositedLayerMapping->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
+        if (compositedScrollsWithRespectTo(layoutObject, *this))
+            compositedLayerMapping->scrollingDisplayItemClientWasInvalidated(displayItemClient, invalidationReason);
+        else
+            compositedLayerMapping->displayItemClientWasInvalidated(displayItemClient, invalidationReason);
     }
 }