Document the ClientRect* vs DOMRect* situation

Source/core/dom/ClientRect.idl

Index: Source/core/dom/ClientRect.idl
diff --git a/Source/core/dom/ClientRect.idl b/Source/core/dom/ClientRect.idl
index 4fae5d7f938242aa57ff41591b32017b15791d1c..f356b39f9423b7c117724ab84baf27ca042464a3 100644
--- a/Source/core/dom/ClientRect.idl
+++ b/Source/core/dom/ClientRect.idl
@@ -24,6 +24,14 @@
  *
  */
 
+// An old version of CSSOM View Module defines the ClientRect interface:
+// http://www.w3.org/TR/2011/WD-cssom-view-20110804/#the-clientrect-interface
+
+// It has since been replaced by DOMRect in CSSOM View Module and
+// Geometry Interfaces Module:
+// http://dev.w3.org/csswg/cssom-view/#extension-to-the-element-interface
+// http://dev.w3.org/fxtf/geometry/#DOMRect
+
 [
     WillBeGarbageCollected,
 ] interface ClientRect {
@@ -34,4 +42,3 @@
     readonly attribute float width;
     readonly attribute float height;
 };
-