Reviewed by Oliver Hunt.

        <video> and <audio> controller should be accessible (edit)
        https://bugs.webkit.org/show_bug.cgi?id=28081

        Test: accessibility/media-element.html

        * GNUmakefile.am:
        * WebCore.gypi:
        * WebCore.pro:
        * WebCore.vcproj/WebCore.vcproj:
        * WebCore.xcodeproj/project.pbxproj:
        * WebCoreSources.bkl:
            Add AccessibilityMediaControls.cpp/.h

        * accessibility/AXObjectCache.cpp:
        * accessibility/AXObjectCache.h:
        (WebCore::AXObjectCache::getOrCreate):
            Create AccessibilityMediaControl. Update Copyright

        * accessibility/AccessibilityMediaControls.cpp:
        * accessibility/AccessibilityMediaControls.h:
            Added.

        * accessibility/AccessibilityObject.cpp:
        * accessibility/AccessibilityObject.h:
            Add isMediaTimeline. Update Copyright.

        * accessibility/AccessibilitySlider.h:
     ...