Clear floats even when they are not tracked by a previous sibling

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

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 883 matching lines @@
     // We should not process floats if the parent node is not a LayoutBlockFlow. Otherwise, we will add
     // floats in an invalid context. This will cause a crash arising from a bad cast on the parent.
     // See <rdar://problem/8049753>, where float property is applied on a text node in a SVG.
     if (!parent() || !parent()->isLayoutBlockFlow())
         return;
 
     // Attempt to locate a previous sibling with overhanging floats. We skip any elements that
     // may have shifted to avoid floats, and any objects whose floats cannot interact with objects
     // outside it (i.e. objects that create a new block formatting context).
     LayoutBlockFlow* parentBlockFlow = toLayoutBlockFlow(parent());
-    bool parentHasFloats = false;
+    bool siblingFloatMayIntrude = false;
     LayoutObject* prev = previousSibling();
     while (prev && (!prev->isBox() || !prev->isLayoutBlock() || toLayoutBlock(prev)->avoidsFloats() || toLayoutBlock(prev)->createsNewFormattingContext())) {
         if (prev->isFloating())
-            parentHasFloats = true;
+            siblingFloatMayIntrude = true;
         prev = prev->previousSibling();
     }
 
     // First add in floats from the parent. Self-collapsing blocks let their parent track any floats that intrude into
-    // them (as opposed to floats they contain themselves) so check for those here too.
+    // them (as opposed to floats they contain themselves) so check for those here too. If margin collapsing has moved
+    // us up past the top a previous sibling then we need to check for floats from the parent too.
     LayoutUnit logicalTopOffset = logicalTop();
-    bool parentHasIntrudingFloats = !parentHasFloats && (!prev || toLayoutBlockFlow(prev)->isSelfCollapsingBlock()) && parentBlockFlow->lowestFloatLogicalBottom() > logicalTopOffset;
-    if (parentHasFloats || parentHasIntrudingFloats)
+    bool parentFloatsMayIntrude = !siblingFloatMayIntrude && (!prev || toLayoutBlockFlow(prev)->isSelfCollapsingBlock() || toLayoutBlock(prev)->logicalTop() > logicalTopOffset)
+        && parentBlockFlow->lowestFloatLogicalBottom() > logicalTopOffset;
+    if (siblingFloatMayIntrude || parentFloatsMayIntrude)
         addIntrudingFloats(parentBlockFlow, parentBlockFlow->logicalLeftOffsetForContent(), logicalTopOffset);
 
     // Add overhanging floats from the previous LayoutBlockFlow, but only if it has a float that intrudes into our space.
     if (prev) {
         LayoutBlockFlow* blockFlow = toLayoutBlockFlow(prev);
         logicalTopOffset -= blockFlow->logicalTop();
         if (blockFlow->lowestFloatLogicalBottom() > logicalTopOffset)
             addIntrudingFloats(blockFlow, LayoutUnit(), logicalTopOffset);
     }
 
@@ skipping 1929 matching lines @@
     FrameView* frameView = document().view();
     LayoutUnit top = LayoutUnit((style()->position() == FixedPosition) ? 0 : frameView->scrollOffset().height());
     int visibleHeight = frameView->visibleContentRect(IncludeScrollbars).height();
     if (size().height() < visibleHeight)
         top += (visibleHeight - size().height()) / 2;
     setY(top);
     dialog->setCentered(top);
 }
 
 } // namespace blink