This fixes a bug that causes the video XBlock parsing to break in the new XBlock runtime if:
* the html5_sources field is set, and
* the download_video field is not set
The error is:
File "/edx/app/edxapp/edx-platform/openedx/core/djangoapps/xblock/rest_api/views.py", line 52, in render_block_view
block = load_block(usage_key, request.user)
File "/edx/app/edxapp/edx-platform/openedx/core/djangoapps/xblock/api.py", line 84, in load_block
return runtime.get_block(usage_key)
File "/edx/app/edxapp/edx-platform/openedx/core/djangoapps/xblock/runtime/blockstore_runtime.py", line 70, in get_block
block = block_class.parse_xml_new_runtime(xml_node, runtime=self, keys=keys)
File "/edx/app/edxapp/edx-platform/common/lib/xmodule/xmodule/video_module/video_module.py", line 620, in parse_xml_new_runtime
setattr(video_block, key, cls.fields[key].from_json(val))
KeyError: 'source'
The reason for the error is that parse_video_xml() will sometimes return a 'source' attribute in its field_data return value, even though source is not a video field (anymore). This then causes an error when trying to look up cls.fields['source']
A workaround in the meantime is to add download_video="false" to the OLX.
d39421d947