Change painting root for squashed layers to the composting container

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index 445b2ad8364fdaf98ac5f7ef66b7d2379952c3da..d150629c601a1795f4fa36f6682c288423b503df 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -1020,6 +1020,10 @@ void CompositedLayerMapping::UpdateSquashingLayerGeometry(
 
   squashing_layer->SetPosition(squash_layer_bounds.Location());
   squashing_layer->SetSize(FloatSize(squash_layer_bounds.Size()));
+  LayoutSize offset_from_layout_object_exclude_subpixel_accumulation = squash_layer_origin_in_compositing_container_space - compositing_container->SubpixelAccumulation();
+  DCHECK(offset_from_layout_object_exclude_subpixel_accumulation.Fraction().IsZero());
+  DCHECK_EQ(owning_layer_.EnclosingLayerWithCompositedLayerMapping(kExcludeSelf), compositing_container);
+  squashing_layer->SetOffsetFromLayoutObject(RoundedIntSize(offset_from_layout_object_exclude_subpixel_accumulation), GraphicsLayer::kDontSetNeedsDisplay);
 
   *offset_from_transformed_ancestor =
       compositing_container_offset_from_transformed_ancestor;
@@ -3004,7 +3008,13 @@ void CompositedLayerMapping::DoPaintTask(
     const IntRect& clip /* In the coords of rootLayer */) const {
   FontCachePurgePreventer font_cache_purge_preventer;
 
+  PaintLayer* painting_root = paint_info.paint_layer;
   IntSize offset = paint_info.offset_from_layout_object;
+  if (paint_info.paint_layer->GetCompositingState() == kPaintsIntoGroupedBacking) {
+    painting_root = owning_layer_.EnclosingLayerWithCompositedLayerMapping(kExcludeSelf);
+    offset = graphics_layer.OffsetFromLayoutObject();
+  }
+
   AffineTransform translation;
   translation.Translate(-offset.Width(), -offset.Height());
   TransformRecorder transform_recorder(context, graphics_layer, translation);
@@ -3016,29 +3026,29 @@ void CompositedLayerMapping::DoPaintTask(
   if (paint_layer_flags & (kPaintLayerPaintingOverflowContents |
                            kPaintLayerPaintingAncestorClippingMaskPhase)) {
     dirty_rect.Move(
-        RoundedIntSize(paint_info.paint_layer->SubpixelAccumulation()));
+        RoundedIntSize(painting_root->SubpixelAccumulation()));
   } else {
     LayoutRect bounds = paint_info.composited_bounds;
-    bounds.Move(paint_info.paint_layer->SubpixelAccumulation());
+    bounds.Move(painting_root->SubpixelAccumulation());
     dirty_rect.Intersect(PixelSnappedIntRect(bounds));
   }
 
 #if DCHECK_IS_ON()
   if (!GetLayoutObject().View()->GetFrame() ||
       !GetLayoutObject().View()->GetFrame()->ShouldThrottleRendering())
-    paint_info.paint_layer->GetLayoutObject().AssertSubtreeIsLaidOut();
+    painting_root->GetLayoutObject().AssertSubtreeIsLaidOut();
 #endif
 
   float device_scale_factor = blink::DeviceScaleFactorDeprecated(
-      paint_info.paint_layer->GetLayoutObject().GetFrame());
+      painting_root->GetLayoutObject().GetFrame());
   context.SetDeviceScaleFactor(device_scale_factor);
 
   if (paint_info.paint_layer->GetCompositingState() !=
       kPaintsIntoGroupedBacking) {
     // FIXME: GraphicsLayers need a way to split for multicol.
     PaintLayerPaintingInfo painting_info(
-        paint_info.paint_layer, LayoutRect(dirty_rect), kGlobalPaintNormalPhase,
-        paint_info.paint_layer->SubpixelAccumulation());
+        painting_root, LayoutRect(dirty_rect), kGlobalPaintNormalPhase,
+        painting_root->SubpixelAccumulation());
     PaintLayerPainter(*paint_info.paint_layer)
         .PaintLayerContents(context, painting_info, paint_layer_flags);
 
@@ -3049,8 +3059,8 @@ void CompositedLayerMapping::DoPaintTask(
               paint_layer_flags | kPaintLayerPaintingOverlayScrollbars);
   } else {
     PaintLayerPaintingInfo painting_info(
-        paint_info.paint_layer, LayoutRect(dirty_rect), kGlobalPaintNormalPhase,
-        paint_info.paint_layer->SubpixelAccumulation());
+        painting_root, LayoutRect(dirty_rect), kGlobalPaintNormalPhase,
+        painting_root->SubpixelAccumulation());
 
     // PaintLayer::paintLayer assumes that the caller clips to the passed rect.
     // Squashed layers need to do this clipping in software, since there is no