MSE: Add layout test for 'decode' error via an algorithm

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 bb839522155b8a2d222ba16f977886464d8a5c76..c69bf83ecb522c8ff759e1496763706194434d23 100644
--- a/LayoutTests/http/tests/media/media-source/mediasource-errors.html
+++ b/LayoutTests/http/tests/media/media-source/mediasource-errors.html
@@ -143,6 +143,28 @@
                     test.done();
                 });
             }, "Signaling 'network' error via endOfStream() after initialization segment has been appended and the HTMLMediaElement has reached HAVE_METADATA.");
+
+            ErrorTest(function(test, mediaElement, mediaSource, segmentInfo, sourceBuffer, mediaData)
+            {
+                assert_equals(mediaElement.readyState, HTMLMediaElement.HAVE_NOTHING);
+
+                var initSegment = MediaSourceUtil.extractSegmentData(mediaData, segmentInfo.init);
+                var mediaSegment = MediaSourceUtil.extractSegmentData(mediaData, segmentInfo.media[0]);
+                var index = (mediaSegment.length + 1) / 5;

[philipj_slow, 2014/11/19 10:08:35]

This and the follow line looks a bit odd, like some finely tuned constants that
need to be documented. I think this is trying to create a buffer that includes
an init segment followed by some corrupt data, right? It looks like mediaData is
already the concatenation of init segment and media data, so why not just
overwrite some of the media data to make it corrupt? I haven't looked at many
MSE test cases before, so I could just be ignorant about how things work.

[jiajia.qin, 2014/11/19 11:57:57]

Yes. I am trying to create a buffer that includes an int segment, partial media
segment(the first 1/5 data is right, but remaining is corrupt data)
I can overwrite some of the media data. But I don't know what kind of data I
should use. Can I just overwrite it using arbitrary number ?  
The test cases before are explicitly calling mediaSource.endofstream() to
trigger the end of stream algorithm. This test case is triggered by an algorithm
which needs to signal a decode error.
( https://w3c.github.io/media-source/#end-of-stream-algorithm )

+                var partialMediaSegment = mediaSegment.subarray(index * 2);
+                mediaData.set(partialMediaSegment, initSegment.length + index);
+
+                test.expectEvent(mediaElement, "error", "mediaElement error.");
+                sourceBuffer.appendBuffer(mediaData);
+
+                test.waitForExpectedEvents(function()
+                {
+                    assert_equals(mediaElement.readyState, HTMLMediaElement.HAVE_METADATA);
+                    assert_true(mediaElement.error != null);
+                    assert_equals(mediaElement.error.code, MediaError.MEDIA_ERR_DECODE);
+                    test.done();
+                });
+            }, "Signaling 'decode' error via segment parser loop algorithm after initialization segment and partial media segment has been appended.");
         </script>
     </body>
 </html>