Only adjust composited pagination position to account for lines offset of inlines.

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

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 23 matching lines @@
 #include "core/frame/Settings.h"
 #include "core/frame/VisualViewport.h"
 #include "core/html/HTMLCanvasElement.h"
 #include "core/html/HTMLIFrameElement.h"
 #include "core/html/HTMLMediaElement.h"
 #include "core/html/HTMLVideoElement.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/layout/LayoutEmbeddedObject.h"
 #include "core/layout/LayoutHTMLCanvas.h"
 #include "core/layout/LayoutImage.h"
+#include "core/layout/LayoutInline.h"
 #include "core/layout/LayoutPart.h"
 #include "core/layout/LayoutVideo.h"
 #include "core/layout/LayoutView.h"
 #include "core/layout/api/LayoutAPIShim.h"
 #include "core/layout/api/LayoutPartItem.h"
 #include "core/layout/compositing/PaintLayerCompositor.h"
 #include "core/loader/resource/ImageResourceContent.h"
 #include "core/page/ChromeClient.h"
 #include "core/page/Page.h"
 #include "core/page/scrolling/ScrollingCoordinator.h"
@@ skipping 823 matching lines @@
   offset.MoveBy(-local_representative_point_for_fragmentation);
   return offset;
 }
 
 void CompositedLayerMapping::ComputeBoundsOfOwningLayer(
     const PaintLayer* composited_ancestor,
     IntRect& local_bounds,
     IntRect& compositing_bounds_relative_to_composited_ancestor,
     LayoutPoint& offset_from_composited_ancestor,
     IntPoint& snapped_offset_from_composited_ancestor) {
-  LayoutRect local_raw_compositing_bounds = CompositedBounds();
+  // HACK(chrishtr): adjust for position of inlines.
+  LayoutPoint local_representative_point_for_fragmentation;
+  if (owning_layer_.GetLayoutObject().IsLayoutInline()) {
+    local_representative_point_for_fragmentation =
+        ToLayoutInline(owning_layer_.GetLayoutObject())
+            .LinesVisualOverflowBoundingBox()

[trchen, 2017/05/16 23:26:47]

LinesVisualOverflowBoundingBox can be expensive (have to collect all descendant
line boxes.). And I'm not sure we actually want to include visual overflow, as
say, wouldn't top-left box shadow cause the same issue?

How about .FirstLineBoxTopLeft() ? Feels like exactly what we want.

[chrishtr, 2017/05/17 02:00:14]

Done, good idea.

+            .Location();
+  }
   offset_from_composited_ancestor = ComputeOffsetFromCompositedAncestor(
       &owning_layer_, composited_ancestor,
-      local_raw_compositing_bounds.Location());
+      local_representative_point_for_fragmentation);
   snapped_offset_from_composited_ancestor =
       IntPoint(offset_from_composited_ancestor.X().Round(),
                offset_from_composited_ancestor.Y().Round());
 
   LayoutSize subpixel_accumulation;
   if (!owning_layer_.Transform() ||
       owning_layer_.Transform()->IsIdentityOrTranslation()) {
     subpixel_accumulation = offset_from_composited_ancestor -
                             snapped_offset_from_composited_ancestor;
   }
   // Otherwise discard the sub-pixel remainder because paint offset can't be
   // transformed by a non-translation transform.
   owning_layer_.SetSubpixelAccumulation(subpixel_accumulation);
 
   // Move the bounds by the subpixel accumulation so that it pixel-snaps
   // relative to absolute pixels instead of local coordinates.
+  LayoutRect local_raw_compositing_bounds = CompositedBounds();
   local_raw_compositing_bounds.Move(subpixel_accumulation);
   local_bounds = PixelSnappedIntRect(local_raw_compositing_bounds);
 
   compositing_bounds_relative_to_composited_ancestor = local_bounds;
   compositing_bounds_relative_to_composited_ancestor.MoveBy(
       snapped_offset_from_composited_ancestor);
 }
 
 void CompositedLayerMapping::UpdateSquashingLayerGeometry(
     const IntPoint& graphics_layer_parent_location,
@@ skipping 2708 matching lines @@
   } else if (graphics_layer == decoration_outline_layer_.get()) {
     name = "Decoration Layer";
   } else {
     NOTREACHED();
   }
 
   return name;
 }
 
 }  // namespace blink