MSE: Speculative fix for flaky mediasource-errors layout test

LayoutTests/http/tests/media/media-source/mediasource-errors.html

Index: LayoutTests/http/tests/media/media-source/mediasource-errors.html
diff --git a/LayoutTests/http/tests/media/media-source/mediasource-errors.html b/LayoutTests/http/tests/media/media-source/mediasource-errors.html
index b9908ad8aebaa389f5875b4049992086ad2369df..3effd166371540b6754353a361fb78dab55cce43 100644
--- a/LayoutTests/http/tests/media/media-source/mediasource-errors.html
+++ b/LayoutTests/http/tests/media/media-source/mediasource-errors.html
@@ -159,7 +159,6 @@
 
                 test.waitForExpectedEvents(function()
                 {
-                    assert_equals(mediaElement.readyState, HTMLMediaElement.HAVE_METADATA);

[philipj_slow, 2015/06/03 09:30:01]

Yeah, this is a very likely cause, there's hardly a single case I can think of
where it's safe to assert anything about readyState or networkState in an event
handler.

                     assert_true(mediaElement.error != null);
                     assert_equals(mediaElement.error.code, MediaError.MEDIA_ERR_DECODE);
                     test.done();