Reduce uses of PassRefPtr in WebCore/dom - 6

Reduce uses of PassRefPtr in WebCore/dom - 6
https://bugs.webkit.org/show_bug.cgi?id=155579

Reviewed by Darin Adler.

* dom/MessagePortChannel.h:
* dom/default/PlatformMessagePortChannel.cpp:
(WebCore::PlatformMessagePortChannel::EventData::EventData):
(WebCore::MessagePortChannel::createChannel):
(WebCore::MessagePortChannel::MessagePortChannel):
(WebCore::MessagePortChannel::postMessageToRemote):
(WebCore::PlatformMessagePortChannel::create):
(WebCore::PlatformMessagePortChannel::PlatformMessagePortChannel):
* dom/default/PlatformMessagePortChannel.h:
(WebCore::PlatformMessagePortChannel::EventData::message):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@198483 268f45cc-cd09-0410-ab3c-d52691b4dbfc