Re-land: bindings: Use MessageEventInit for MessageEvent constructor

Source/core/dom/MessagePort.cpp

Index: Source/core/dom/MessagePort.cpp
diff --git a/Source/core/dom/MessagePort.cpp b/Source/core/dom/MessagePort.cpp
index ebb399f19274ca7a7496ba59af3dda169f646bf1..3df2fde8f052b25304b7ab5fc42c341e3a839d97 100644
--- a/Source/core/dom/MessagePort.cpp
+++ b/Source/core/dom/MessagePort.cpp
@@ -259,8 +259,10 @@ PassOwnPtr<MessagePortChannelArray> MessagePort::disentanglePorts(ExecutionConte
 
 PassOwnPtrWillBeRawPtr<MessagePortArray> MessagePort::entanglePorts(ExecutionContext& context, PassOwnPtr<MessagePortChannelArray> channels)
 {
+    // https://html.spec.whatwg.org/multipage/comms.html#message-ports
+    // |ports| should be an empty array, not null even when there is no ports.
     if (!channels || !channels->size())
-        return nullptr;
+        return adoptPtrWillBeNoop(new MessagePortArray());
 
     OwnPtrWillBeRawPtr<MessagePortArray> portArray = adoptPtrWillBeNoop(new MessagePortArray(channels->size()));
     for (unsigned i = 0; i < channels->size(); ++i) {