Special-case LocalDOMWindow for same-origin access in bindings.

third_party/WebKit/Source/bindings/IDLExtendedAttributes.md

Index: third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
diff --git a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
index 9d5dd81304b186b575fed42eeb257db22b6a2ae9..8b4dbc7dc74bfd9e02af7f29e82592651db8bef6 100644
--- a/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
+++ b/third_party/WebKit/Source/bindings/IDLExtendedAttributes.md
@@ -1478,6 +1478,20 @@ reads would leak cross-origin information.
 With both `Getter` and `Setter`, allows both cross-origin reads and cross-origin
 writes. This is used for the `Window.location` attribute.
 
+### [SameOriginImplementedAs] _(i)
+
+Summary: Used in conjunction with (#_CrossOrigin_i). Allows a different C++
+class to be used for a same-origin access.
+
+Usage for interfaces:
+```webidl
+[
+    SameOriginImplementedAs=LocalDOMWindow,
+] interface Window {
+    ...
+};
+```
+
 ### [CustomConstructor] _(i)_
 
 Summary: They allow you to write custom bindings for constructors.