When accessing line boxes, use RenderBlockFlow instead of RenderBlock.

Source/core/rendering/RenderBlockFlow.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2003-2013 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  * 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
@@ skipping 68 matching lines @@
     {
         return style()->isLeftToRightDirection() ? logicalLeftOffsetForLine(position, shouldIndentText, logicalHeight)
             : logicalWidth() - logicalRightOffsetForLine(position, shouldIndentText, logicalHeight);
     }
     LayoutUnit endOffsetForLine(LayoutUnit position, bool shouldIndentText, LayoutUnit logicalHeight = 0) const
     {
         return !style()->isLeftToRightDirection() ? logicalLeftOffsetForLine(position, shouldIndentText, logicalHeight)
             : logicalWidth() - logicalRightOffsetForLine(position, shouldIndentText, logicalHeight);
     }
 
+    // FIXME-BLOCKFLOW: Move this into RenderBlockFlow once there are no calls

[Julien - ping for review, 2014/07/18 21:10:50]

I think we should tie that to a bug if we have one.

+    // in RenderBlock.
+    using RenderBlock::lineBoxes;
+    using RenderBlock::firstLineBox;
+    using RenderBlock::lastLineBox;
+    using RenderBlock::firstRootBox;
+    using RenderBlock::lastRootBox;
+
     virtual LayoutUnit logicalLeftSelectionOffset(RenderBlock* rootBlock, LayoutUnit position) OVERRIDE;
     virtual LayoutUnit logicalRightSelectionOffset(RenderBlock* rootBlock, LayoutUnit position) OVERRIDE;
 
     LayoutUnit computeStartPositionDeltaForChildAvoidingFloats(const RenderBox* child, LayoutUnit childMarginStart);
 
     RootInlineBox* createAndAppendRootInlineBox();
 
     void markAllDescendantsWithFloatsForLayout(RenderBox* floatToRemove = 0, bool inLayout = true);
     void markSiblingsWithFloatsForLayout(RenderBox* floatToRemove = 0);
 
@@ skipping 399 matching lines @@
 
 // END METHODS DEFINED IN RenderBlockLineLayout
 
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderBlockFlow, isRenderBlockFlow());
 
 } // namespace WebCore
 
 #endif // RenderBlockFlow_h