No need to detect change in size when opting for PositionedMovementLayout

Source/core/rendering/style/RenderStyle.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 335 matching lines @@
 
 bool RenderStyle::inheritedDataShared(const RenderStyle* other) const
 {
     // This is a fast check that only looks if the data structures are shared.
     return inherited_flags == other->inherited_flags
         && inherited.get() == other->inherited.get()
         && m_svgStyle.get() == other->m_svgStyle.get()
         && rareInheritedData.get() == other->rareInheritedData.get();
 }
 
-static bool positionedObjectMovedOnly(const LengthBox& a, const LengthBox& b, const Length& width)
-{
-    // If any unit types are different, then we can't guarantee
-    // that this was just a movement.
-    if (a.left().type() != b.left().type()
-        || a.right().type() != b.right().type()
-        || a.top().type() != b.top().type()
-        || a.bottom().type() != b.bottom().type())
-        return false;
-
-    // Only one unit can be non-auto in the horizontal direction and
-    // in the vertical direction.  Otherwise the adjustment of values
-    // is changing the size of the box.
-    if (!a.left().isIntrinsicOrAuto() && !a.right().isIntrinsicOrAuto())
-        return false;
-    if (!a.top().isIntrinsicOrAuto() && !a.bottom().isIntrinsicOrAuto())
-        return false;
-    // If our width is auto and left or right is specified and changed then this
-    // is not just a movement - we need to resize to our container.
-    if (width.isIntrinsicOrAuto()
-        && ((!a.left().isIntrinsicOrAuto() && a.left() != b.left())
-            || (!a.right().isIntrinsicOrAuto() && a.right() != b.right())))
-        return false;
-
-    // One of the units is fixed or percent in both directions and stayed
-    // that way in the new style.  Therefore all we are doing is moving.
-    return true;
-}
-
 StyleDifference RenderStyle::visualInvalidationDiff(const RenderStyle& other) const
 {
     // Note, we use .get() on each DataRef below because DataRef::operator== will do a deep
     // compare, which is duplicate work when we're going to compare each property inside
     // this function anyway.
 
     StyleDifference diff;
     if (m_svgStyle.get() != other.m_svgStyle.get())
         diff = m_svgStyle->diff(other.m_svgStyle.get());
 
     if ((!diff.needsFullLayout() || !diff.needsPaintInvalidation()) && diffNeedsFullLayoutAndPaintInvalidation(other)) {
         diff.setNeedsFullLayout();
         diff.setNeedsPaintInvalidationObject();
     }
 
     if (!diff.needsFullLayout() && diffNeedsFullLayout(other))
         diff.setNeedsFullLayout();
 
     if (!diff.needsFullLayout() && surround->margin != other.surround->margin) {
         // Relative-positioned elements collapse their margins so need a full layout.
         if (position() == AbsolutePosition || position() == FixedPosition)
             diff.setNeedsPositionedMovementLayout();
         else
             diff.setNeedsFullLayout();
     }
 
     if (!diff.needsFullLayout() && position() != StaticPosition && surround->offset != other.surround->offset) {
         // Optimize for the case where a positioned layer is moving but not changing size.

[pdr., 2014/12/01 21:03:05]

This comment needs updating, no?

-        if (positionedObjectMovedOnly(surround->offset, other.surround->offset, m_box->width()))
-            diff.setNeedsPositionedMovementLayout();
-        else
-            diff.setNeedsFullLayout();
+        diff.setNeedsPositionedMovementLayout();
     }
 
     if (diffNeedsPaintInvalidationLayer(other))
         diff.setNeedsPaintInvalidationLayer();
     else if (diffNeedsPaintInvalidationObject(other))
         diff.setNeedsPaintInvalidationObject();
 
     updatePropertySpecificDifferences(other, diff);
 
     // Cursors are not checked, since they will be set appropriately in response to mouse events,
@@ skipping 1333 matching lines @@
         horizontal || includeLogicalRightEdge);
 
     edges[BSLeft] = BorderEdge(borderLeftWidth(),
         visitedDependentColor(CSSPropertyBorderLeftColor),
         borderLeftStyle(),
         borderLeftIsTransparent(),
         !horizontal || includeLogicalLeftEdge);
 }
 
 } // namespace blink