Clear floats that are nested in previous siblings and don't overhang.

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

Index: third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
index 3f9c12f381a38e37c3da6530c8d553774887fc86..0e1a6b06a6ea29b89ef1827cdc57527b7da61b3f 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.cpp
@@ -429,6 +429,8 @@ inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren, LayoutUnit &
             // TODO(robhogan): We should exclude blocks that create formatting contexts, not just out of flow or floating blocks.
             if (child->isLayoutBlockFlow() && !child->isFloatingOrOutOfFlowPositioned()) {
                 LayoutBlockFlow* block = toLayoutBlockFlow(child);
+                if (!block->containsFloats())
+                    continue;
                 lowestBlock = block;
                 if (oldHeight <= newHeight || block->lowestFloatLogicalBottom() + block->logicalTop() <= newHeight)
                     break;
@@ -436,6 +438,8 @@ inline bool LayoutBlockFlow::layoutBlockFlow(bool relayoutChildren, LayoutUnit &
                 addedOverhangingFloats = true;
             }
         }
+        // If we have no overhanging floats we still pass a record of the lowest non-overhanging float up the tree so we can enclose it if
+        // we are a formatting context and allow siblings to avoid it if they have negative margin and find themselves in its vicinity.
         if (!addedOverhangingFloats)
             addLowestFloatFromChildren(lowestBlock);
     }