Make InlineBox::renderer() and related subclass methods return reference.

Source/core/rendering/RootInlineBox.h

Index: Source/core/rendering/RootInlineBox.h
diff --git a/Source/core/rendering/RootInlineBox.h b/Source/core/rendering/RootInlineBox.h
index 92ea13091364096a42a5038ace84a5e3a89a1bb8..32b1c55221d0ee4da61fd42fe4d73b80f0639c37 100644
--- a/Source/core/rendering/RootInlineBox.h
+++ b/Source/core/rendering/RootInlineBox.h
@@ -35,7 +35,7 @@ struct GapRects;
 
 class RootInlineBox : public InlineFlowBox {
 public:
-    explicit RootInlineBox(RenderBlockFlow*);
+    explicit RootInlineBox(RenderBlockFlow&);
 
     virtual void destroy() OVERRIDE FINAL;
 
@@ -125,7 +125,7 @@ public:
 
     GapRects lineSelectionGap(RenderBlock* rootBlock, const LayoutPoint& rootBlockPhysicalPosition, const LayoutSize& offsetFromRootBlock, LayoutUnit selTop, LayoutUnit selHeight, const PaintInfo*);
 
-    RenderBlockFlow* block() const;
+    RenderBlockFlow& block() const;
 
     InlineBox* closestLeafChildForPoint(const IntPoint&, bool onlyEditableLeaves);
     InlineBox* closestLeafChildForLogicalLeftPosition(int, bool onlyEditableLeaves = false);