Compute positioned elements width correctly when it has anonymous ancestors

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2834 matching lines @@
         if (FrameView* frameView = view->frameView()) {
             // Don't use visibleContentRect since the PaintLayer's size has not been set yet.
             IntSize viewportSize = frameView->layoutViewportScrollableArea()->excludeScrollbars(frameView->frameRect().size());
             return containingBlock->isHorizontalWritingMode() ? viewportSize.width() : viewportSize.height();
         }
     }
 
     if (hasOverrideContainingBlockLogicalWidth())
         return overrideContainingBlockContentLogicalWidth();
 
-    if (containingBlock->isBox())
+    // Ensure we compute our width based on the width of our rel-pos inline container rather than any anonymous block
+    // created to manage a block-flow ancestor of ours in the rel-pos inline's inline flow.
+    if (containingBlock->isAnonymousBlock() && containingBlock->isRelPositioned())
+        containingBlock = toLayoutBox(containingBlock)->continuation();
+    else if (containingBlock->isBox())
         return std::max(LayoutUnit(), toLayoutBox(containingBlock)->clientLogicalWidth());
 
     ASSERT(containingBlock->isLayoutInline() && containingBlock->isInFlowPositioned());
 
     const LayoutInline* flow = toLayoutInline(containingBlock);
     InlineFlowBox* first = flow->firstLineBox();
     InlineFlowBox* last = flow->lastLineBox();
 
     // If the containing block is empty, return a width of 0.
     if (!first || !last)
@@ skipping 1982 matching lines @@
     StyleImage* borderImage = style()->borderImage().image();
     return borderImage && borderImage->canRender(*this, style()->effectiveZoom()) && borderImage->isLoaded();
 }
 
 ShapeOutsideInfo* LayoutBox::shapeOutsideInfo() const
 {
     return ShapeOutsideInfo::isEnabledFor(*this) ? ShapeOutsideInfo::info(*this) : nullptr;
 }
 
 } // namespace blink