Add CaretBase::m_caretPainter, and compute caretBrowsing lazily.

Source/core/editing/FrameSelection.h

Index: Source/core/editing/FrameSelection.h
diff --git a/Source/core/editing/FrameSelection.h b/Source/core/editing/FrameSelection.h
index 0df951faa2d51d540e6ea7e41470a20782a75175..be36da968d9b18abbaa760ebf900c9a126892fd3 100644
--- a/Source/core/editing/FrameSelection.h
+++ b/Source/core/editing/FrameSelection.h
@@ -147,7 +147,7 @@ public:
     Position end() const { return m_selection.end(); }
 
     // Return the layoutObject that is responsible for painting the caret (in the selection start node)
-    LayoutBlock* caretLayoutObject() const;
+    LayoutBlock* caretLayoutObject() const { return CaretBase::caretPainter(); }
 
     // Bounds of (possibly transformed) caret in absolute coords
     IntRect absoluteCaretBounds();