I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

*/
/**
 * Page text marked content part.
 *
 * @typedef {Object} TextMarkedContent
 * @property {string} type - Either 'beginMarkedContent',
 *   'beginMarkedContentProps', or 'endMarkedContent'.
 * @property {string} id - The marked content identifier. Only used for type
 *   'beginMarkedContentProps'.
 */
/**
 * Text style.
 *
 * @typedef {Object} TextStyle
 * @property {number} ascent - Font ascent.
 * @property {number} descent - Font descent.
 * @property {boolean} vertical - Whether or not the text is in vertical mode.
 * @property {string} fontFamily - The possible font family.
 */
/**
 * Page annotation parameters.
 *
 * @typedef {Object} GetAnnotationsParameters
 * @property {string} intent - Determines the annotations that will be fetched,
 *   can be either 'display' (viewable annotations) or 'print' (printable
 *   annotations). If the parameter is omitted, all annotations are fetched.
 */
/**
 * Page render parameters.
 *