Reviewed by Eric Carlson.

        Media layout tests should have a way to provide test files in different formats
        https://bugs.webkit.org/show_bug.cgi?id=28327

        Added media-file.js which has a findMediaFile(type, name) method
        to find a proper media file to load according to supported codecs.

        Also changed 10 layout tests to use above method to locate the test file.

        * media/controls-strict.html: Use findMediaFile(type, name).
        * media/controls-styling.html: ditto.
        * media/media-file.js: Added. Provide findMediaFile(type, name).
        * media/video-append-source.html: Use findMediaFile(type, name).
        * media/video-aspect-ratio.html: ditto.
        * media/video-autoplay.html: ditto.
        * media/video-buffered.html: ditto.
        * media/video-controls-rendering.html: ditto.
        * media/video-layer-crash.html: ditto.
        * media/video-transformed.html: Use findMediaFile(type, name).
        * media/video-zoom-controls.html: ditto.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@48237 268f45cc-cd09-0410-ab3c-d52691b4dbfc