Round the subpixel accumulation used for composited scrolling content

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..82099422afca6333172560eac643a19656facc21 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -3035,10 +3035,18 @@ void CompositedLayerMapping::DoPaintTask(
 
   if (paint_info.paint_layer->GetCompositingState() !=
       kPaintsIntoGroupedBacking) {
+    LayoutSize sub_pixel_accumulation =
+        paint_info.paint_layer->SubpixelAccumulation();
+    if (paint_layer_flags & kPaintLayerPaintingCompositingScrollingPhase) {
+      // The composited scrolling contents layer position rounds the subpixel
+      // accumulation.
+      sub_pixel_accumulation =
+          LayoutSize(RoundedIntSize(sub_pixel_accumulation));
+    }
     // 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());
+        sub_pixel_accumulation);
     PaintLayerPainter(*paint_info.paint_layer)
         .PaintLayerContents(context, painting_info, paint_layer_flags);