Reduce amount of platform specific code in MessagePortChannel
        https://bugs.webkit.org/show_bug.cgi?id=112469

        Reviewed by Sam Weinig.

        * dom/MessagePortChannel.h: Ifdefed out an unused channel() function, except for
        Chromium, where it is used. We certainly don't want to expose this implementation
        detail as a public function.

        * dom/default/PlatformMessagePortChannel.h: Removed functions that are no longer
        delegated. Made class contents all public, as it's now basically a data storage
        for MessagePortChannel.

        * dom/default/PlatformMessagePortChannel.cpp:
        (WebCore::MessagePortChannel::createChannel):
        (WebCore::MessagePortChannel::~MessagePortChannel):
        (WebCore::MessagePortChannel::entangleIfOpen):
        (WebCore::MessagePortChannel::disentangle):
        (WebCore::MessagePortChannel::postMessageToRemote):
        (WebCore::MessagePortChannel::tryGetMessageFromRemote):
        (WebCore::MessagePortChannel::close):
        (WebCore::MessagePortChannel::isConnectedTo):
        (WebCore::MessagePortChannel::hasPendingActivity):
        (WebCore::MessagePortChannel::locallyEntangledPort):
        (WebCore::PlatformMessagePortChannel::PlatformMessagePortChannel):
        (WebCore::PlatformMessagePortChannel::entangledChannel):
        Moved code from PlatformMessagePortChannel to MessagePortChannel. Added some
        FIXMEs.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145965 268f45cc-cd09-0410-ab3c-d52691b4dbfc