Reduce the number of compositing test failures

Reduce the number of compositing test failures
https://bugs.webkit.org/show_bug.cgi?id=76495

Reviewed by James Robinson.

General cleanup of compositing tests:
    * video tests now do a seek to guarantee that the pixel result will show a frame
    * video tests use a shared JS file (can't use media/video-test.js because it always
    calls dumpAsText(), which is not reversible).
    * ideo-with-invalid-source.html fixed to use a file extension so that the
    error event fires (bug 76494).
    * pixel results rebaselined.

* compositing/geometry/clipped-video-controller.html:
* compositing/geometry/video-fixed-scrolling.html:
* compositing/geometry/video-opacity-overlay.html:
* compositing/layers-inside-overflow-scroll.html:
* compositing/overflow/scroll-ancestor-update.html:
* compositing/reflections/load-video-in-reflection.html:
* compositing/resources/media-testing.js: Added.
(ensureFrameVisible):
* compositing/self-painting-layers.html:
* compositing/video/video-with-invalid-source.html:
* compositing/visibility/visibility-simple-video-layer.html:
* platform/mac/compositing/color-matching/image-color-matching-expected.png:
* platform/mac/compositing/geometry/video-fixed-scrolling-expected.png:
* platform/mac/compositing/geometry/video-opacity-overlay-expected.png:
* platform/mac/compositing/layers-inside-overflow-scroll-expected.png:
* platform/mac/compositing/overflow/scroll-ancestor-update-expected.png:
* platform/mac/compositing/overflow/scroll-ancestor-update-expected.txt:
* platform/mac/compositing/plugins/composited-plugin-expected.png:
* platform/mac/compositing/reflections/load-video-in-reflection-expected.png:
* platform/mac/compositing/reflections/simple-composited-reflections-expected.png:
* platform/mac/compositing/self-painting-layers-expected.png:
* platform/mac/compositing/video/video-background-color-expected.png:
* platform/mac/test_expectations.txt:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@105219 268f45cc-cd09-0410-ab3c-d52691b4dbfc