When placing a float, pay attention to its final logical top.

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 3614 matching lines @@
         std::max(logicalTopForFloat(*lastPlacedFloatingObject), logicalTop);
 
   FloatingObjectSetIterator end = floatingObjectSet.end();
   // Now walk through the set of unpositioned floats and place them.
   for (; it != end; ++it) {
     FloatingObject& floatingObject = *it->get();
     // The containing block is responsible for positioning floats, so if we have
     // unplaced floats in our list that come from somewhere else, we have a bug.
     DCHECK_EQ(floatingObject.layoutObject()->containingBlock(), this);
 
-    positionAndLayoutFloat(floatingObject, logicalTop);
+    logicalTop = positionAndLayoutFloat(floatingObject, logicalTop);
 
     m_floatingObjects->addPlacedObject(floatingObject);
 
     if (width)
       width->shrinkAvailableWidthForNewFloatIfNeeded(floatingObject);
   }
   return true;
 }
 
 LayoutUnit LayoutBlockFlow::positionAndLayoutFloat(
@@ skipping 924 matching lines @@
   return LayoutBlock::invalidatePaintIfNeeded(paintInvalidationState);
 }
 
 void LayoutBlockFlow::invalidateDisplayItemClients(
     PaintInvalidationReason invalidationReason) const {
   BlockFlowPaintInvalidator(*this).invalidateDisplayItemClients(
       invalidationReason);
 }
 
 }  // namespace blink