Add marginBeforeIfFloating() to LayoutBlockFlow.

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

Index: third_party/WebKit/Source/core/layout/LayoutBlockFlow.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.h b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.h
index cb05410917234bff2c63973dbaba79c4e1321044..ca222c0e6ab01386fc3a7147e1902dc126cb3db9 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlockFlow.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBlockFlow.h
@@ -516,6 +516,10 @@ private:
     LayoutUnit collapsedMarginBefore() const final { return maxPositiveMarginBefore() - maxNegativeMarginBefore(); }
     LayoutUnit collapsedMarginAfter() const final { return maxPositiveMarginAfter() - maxNegativeMarginAfter(); }
 
+    // Floats' margins do not collapse with page or column boundaries, and we therefore need to
+    // treat them specially in some cases.
+    LayoutUnit marginBeforeIfFloating() const { return isFloating() ? marginBefore() : LayoutUnit(); }
+
     LayoutUnit collapseMargins(LayoutBox& child, MarginInfo&, bool childIsSelfCollapsing, bool childDiscardMarginBefore, bool childDiscardMarginAfter);
     LayoutUnit clearFloatsIfNeeded(LayoutBox& child, MarginInfo&, LayoutUnit oldTopPosMargin, LayoutUnit oldTopNegMargin, LayoutUnit yPos, bool childIsSelfCollapsing, bool childDiscardMargin);
     LayoutUnit estimateLogicalTopPosition(LayoutBox& child, const MarginInfo&, LayoutUnit& estimateWithoutPagination);