Add comment about CaretBase::updateCaretRect.

Source/core/editing/Caret.h

Index: Source/core/editing/Caret.h
diff --git a/Source/core/editing/Caret.h b/Source/core/editing/Caret.h
index 728f36e852e7cc07caa0ee9adfdaa5f4687d692c..674adf01ba8db39b46aea3a17f94adb1b27ea7a7 100644
--- a/Source/core/editing/Caret.h
+++ b/Source/core/editing/Caret.h
@@ -48,8 +48,10 @@ protected:
 
     void invalidateCaretRect(Node*, bool caretRectChanged = false);
     void clearCaretRect();
+    // Creating VisiblePosition causes synchronous layout so we should use the
+    // PositionWithAffinity version if possible.
+    // A position in HTMLTextFromControlElement is a typical example.
     bool updateCaretRect(Document*, const PositionWithAffinity& caretPosition);
-    // Simply calls above updateCaretRect using deepEquivalent() and affinity().
     bool updateCaretRect(Document*, const VisiblePosition& caretPosition);
     IntRect absoluteBoundsForLocalRect(Node*, const LayoutRect&) const;
     bool shouldRepaintCaret(const RenderView*, bool isContentEditable) const;