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)

return this._internalRenderTask.capability.promise;
  }
  /**
   * Cancels the rendering task. If the task is currently rendering it will
   * not be cancelled until graphics pauses with a timeout. The promise that
   * this object extends will be rejected when cancelled.
   */
  cancel() {
    this._internalRenderTask.cancel();
  }
}
/**
 * For internal use only.
 * @ignore
 */
const InternalRenderTask = (function InternalRenderTaskClosure() {
  const canvasInRendering = new WeakSet();
  
  class InternalRenderTask {
    constructor({