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)

*
 * @typedef {Object} getTextContentParameters
 * @property {boolean} normalizeWhitespace - Replaces all occurrences of
 *   whitespace with standard spaces (0x20). The default value is `false`.
 * @property {boolean} disableCombineTextItems - Do not attempt to combine
 *   same line {@link TextItem}'s. The default value is `false`.
 * @property {boolean} [includeMarkedContent] - When true include marked
 *   content items in the items array of TextContent. The default is `false`.
 */
/**
 * Page text content.
 *
 * @typedef {Object} TextContent
 * @property {Array<TextItem | TextMarkedContent>} items - Array of
 *   {@link TextItem} and {@link TextMarkedContent} objects. TextMarkedContent
 *   items are included when includeMarkedContent is true.
 * @property {Object<string, TextStyle>} styles - {@link TextStyle} objects,
 *   indexed by font name.
 */
/**
 * Page text content part.
 *
 * @typedef {Object} TextItem
 * @property {string} str - Text content.
 * @property {string} dir - Text direction: 'ttb', 'ltr' or 'rtl'.
 * @property {Array<any>} transform - Transformation matrix.
 * @property {number} width - Width in device space.
 * @property {number} height - Height in device space.
 * @property {string} fontName - Font name used by PDF.js for converted font.
 *