Round the subpixel accumulation used for composited scrolling content

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

Index: third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
index 8504021eea4c5e77618401dfd9af5fa839648687..9a190866b3fa96f731d6bf53f4959e15689d6159 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerPainter.cpp
@@ -47,6 +47,8 @@ void PaintLayerPainter::Paint(GraphicsContext& context,
                               const LayoutRect& damage_rect,
                               const GlobalPaintFlags global_paint_flags,
                               PaintLayerFlags paint_flags) {
+  DCHECK(paint_layer_.GetCompositingState() != kPaintsIntoOwnBacking ||
+         paint_layer_.SubpixelAccumulation().IsZero());
   PaintLayerPaintingInfo painting_info(
       &paint_layer_, LayoutRect(EnclosingIntRect(damage_rect)),
       global_paint_flags, LayoutSize());
@@ -329,10 +331,6 @@ PaintResult PaintLayerPainter::PaintLayerContents(
   // Ensure our lists are up to date.
   paint_layer_.StackingNode()->UpdateLayerListsIfNeeded();
 
-  LayoutSize subpixel_accumulation =
-      paint_layer_.GetCompositingState() == kPaintsIntoOwnBacking
-          ? paint_layer_.SubpixelAccumulation()
-          : painting_info_arg.sub_pixel_accumulation;
   ShouldRespectOverflowClipType respect_overflow_clip =
       ShouldRespectOverflowClip(paint_flags, paint_layer_.GetLayoutObject());
 
@@ -341,7 +339,8 @@ PaintResult PaintLayerPainter::PaintLayerContents(
   if (ShouldCreateSubsequence(paint_layer_, context, painting_info_arg,
                               paint_flags)) {
     if (!ShouldRepaintSubsequence(paint_layer_, painting_info_arg,
-                                  respect_overflow_clip, subpixel_accumulation,
+                                  respect_overflow_clip,
+                                  painting_info_arg.sub_pixel_accumulation,
                                   should_clear_empty_paint_phase_flags) &&
         SubsequenceRecorder::UseCachedSubsequenceIfPossible(context,
                                                             paint_layer_))
@@ -362,7 +361,7 @@ PaintResult PaintLayerPainter::PaintLayerContents(
 
   LayoutPoint offset_from_root;
   paint_layer_.ConvertToLayerCoords(painting_info.root_layer, offset_from_root);
-  offset_from_root.Move(subpixel_accumulation);
+  offset_from_root.Move(painting_info_arg.sub_pixel_accumulation);
 
   LayoutRect bounds = paint_layer_.PhysicalBoundingBox(offset_from_root);
   if (!painting_info.paint_dirty_rect.Contains(bounds))
@@ -418,8 +417,6 @@ PaintResult PaintLayerPainter::PaintLayerContents(
   }
 
   PaintLayerPaintingInfo local_painting_info(painting_info);
-  local_painting_info.sub_pixel_accumulation = subpixel_accumulation;
-
   bool should_paint_content = paint_layer_.HasVisibleContent() &&
                               is_self_painting_layer &&
                               !is_painting_overlay_scrollbars;
@@ -1241,6 +1238,8 @@ void PaintLayerPainter::PaintOverlayScrollbars(
   if (!paint_layer_.ContainsDirtyOverlayScrollbars())
     return;
 
+  DCHECK(paint_layer_.GetCompositingState() != kPaintsIntoOwnBacking ||
+         paint_layer_.SubpixelAccumulation().IsZero());
   PaintLayerPaintingInfo painting_info(
       &paint_layer_, LayoutRect(EnclosingIntRect(damage_rect)), paint_flags,
       LayoutSize());