Paint flex items atomically, like inline-blocks

Source/core/rendering/RenderBlock.h

Index: Source/core/rendering/RenderBlock.h
diff --git a/Source/core/rendering/RenderBlock.h b/Source/core/rendering/RenderBlock.h
index 24cc7472c7b08f796ac5f23eb90d7ffc64825d03..1293c5aece494e81c827133d71cf61fd6887ec11 100644
--- a/Source/core/rendering/RenderBlock.h
+++ b/Source/core/rendering/RenderBlock.h
@@ -454,6 +454,10 @@ public:
     bool allowsShapeInsideInfoSharing() const { return !isInline() && !isFloating(); }
     virtual void imageChanged(WrappedImagePtr, const IntRect* = 0) OVERRIDE;
 
+    // inline-block elements paint all phases atomically. This function ensures that. Certain other elements
+    // (grid items, flex items) require this behavior as well, and this function exists as a helper for them.
+    // It is expected that the caller will call this function independent of the value of paintInfo.phase.
+    static void paintAsInlineBlock(RenderObject*, PaintInfo&, const LayoutPoint&);
 protected:
     virtual void willBeDestroyed();
 
@@ -498,6 +502,7 @@ protected:
     virtual void paintObject(PaintInfo&, const LayoutPoint&);
     virtual void paintChildren(PaintInfo&, const LayoutPoint&);
     void paintChild(RenderBox*, PaintInfo&, const LayoutPoint&);
+    void paintChildAsInlineBlock(RenderBox*, PaintInfo&, const LayoutPoint&);
 
     LayoutUnit logicalRightOffsetForLine(LayoutUnit logicalTop, LayoutUnit fixedOffset, bool applyTextIndent, LayoutUnit* heightRemaining = 0, LayoutUnit logicalHeight = 0) const
     {