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)

* @property {PDFFindController} [findController] - The find controller
 *   component.
 * @property {PDFScriptingManager} [scriptingManager] - The scripting manager
 *   component.
 * @property {PDFRenderingQueue} [renderingQueue] - The rendering queue object.
 * @property {boolean} [removePageBorders] - Removes the border shadow around
 *   the pages. The default value is `false`.
 * @property {number} [textLayerMode] - Controls if the text layer used for
 *   selection and searching is created, and if the improved text selection
 *   behaviour is enabled. The constants from {TextLayerMode} should be used.
 *   The default value is `TextLayerMode.ENABLE`.
 * @property {string} [imageResourcesPath] - Path for image resources, mainly
 *   mainly for annotation icons. Include trailing slash.
 * @property {boolean} [renderInteractiveForms] - Enables rendering of
 *   interactive form elements. The default value is `true`.
 * @property {boolean} [enablePrintAutoRotate] - Enables automatic rotation of
 *   landscape pages upon printing. The default is `false`.
 * @property {string} renderer - 'canvas' or 'svg'. The default is 'canvas'.
 * @property {boolean} [enableWebGL] - Enables WebGL accelerated rendering for
 *   some operations. The default value is `false`.
 * @property {boolean} [useOnlyCssZoom] - Enables CSS only zooming. The default
 *   value is `false`.
 * @property {number} [maxCanvasPixels] - The maximum supported canvas size in
 *   total pixels, i.e. width * height. Use -1 for no limit. The default value
 *   is 4096 * 4096 (16 mega-pixels).
 * @property {IL10n} l10n - Localization service.
 * @property {boolean} [enableScripting] - Enable embedded script execution
 *   (also requires {scriptingManager} being set). The default value is `false`.
 */
function PDFPageViewBuffer(size) {