Reviewed by Tony Gentilcore.

        Media Stream API: adding Stream and GeneratedStream classes.
        https://bugs.webkit.org/show_bug.cgi?id=56666

        Add the code for the Stream and GeneratedStream classes and integrate it
        with the existing stream generation requests.

        Tests for the Media Stream API will be provided by the bug 56587.

        * CMakeLists.txt:
        * CodeGenerators.pri:
        * DerivedSources.cpp:
        * DerivedSources.make:
        * GNUmakefile.list.am:
        * WebCore.gypi:
        * WebCore.pro:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:
        * bindings/js/JSEventTarget.cpp:
        (WebCore::toJS):
        * bindings/v8/V8DOMWrapper.cpp:
        (WebCore::V8DOMWrapper::convertEventTargetToV8Object):
        * dom/DOMAllInOne.cpp:
        * dom/EventTarget.cpp:
        (WebCore::EventTarget::toStream):
        (WebCore::EventTarget::t...