[css-flexbox] Correctly implement contain: size on a flex item

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 692 matching lines @@
     if (!object->hasOverflowClip())
         return false;
 
     if (object->style()->width().isIntrinsicOrAuto() || object->style()->height().isIntrinsicOrAuto() || object->style()->height().hasPercent())
         return false;
 
     // Scrollbar parts can be removed during layout. Avoid the complexity of having to deal with that.
     if (object->isLayoutScrollbarPart())
         return false;
 
+    // In general we can't relayout a flex item independently of its container; not only is the result
+    // incorrect due to the override size that's set, it also messes with the cached main size on the flexbox.
+    if (object->isBox() && toLayoutBox(object)->isFlexItem())
+        return false;
+
     // Inside multicol it's generally problematic to allow relayout roots. The multicol container
     // itself may be scheduled for relayout as well (due to other changes that may have happened
     // since the previous layout pass), which might affect the column heights, which may affect how
     // this object breaks across columns). Spanners may also have been added or removed since the
     // previous layout pass, which is just another way of affecting the column heights (and the
     // number of rows). Instead of identifying cases where it's safe to allow relayout roots, just
     // disallow them inside multicol.
     if (object->isInsideFlowThread())
         return false;
 
@@ skipping 2922 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
     }
 }
 
 #endif