binding: Adds layout tests to check origins of window.postMessage

third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp

Index: third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
diff --git a/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp b/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
index 730dd279d54f78797565f1c0ed8ca18ecb84ec9e..4725c465cadedac1acd56151d22cfb18d2c251b2 100644
--- a/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
+++ b/third_party/WebKit/Source/bindings/core/v8/custom/V8WindowCustom.cpp
@@ -173,6 +173,10 @@ void V8Window::postMessageMethodCustom(const v8::FunctionCallbackInfo<v8::Value>
     // None of these need to be RefPtr because info and context are guaranteed
     // to hold on to them.
     DOMWindow* window = V8Window::toImpl(info.Holder());
+    // TODO(yukishiino): The HTML spec specifies that we should use the
+    // Incumbent Realm instead of the Current Realm, but currently we don't have
+    // a way to retrieve the Incumbent Realm.  See also:
+    // https://html.spec.whatwg.org/multipage/comms.html#dom-window-postmessage
     LocalDOMWindow* source = currentDOMWindow(info.GetIsolate());
 
     ASSERT(window);