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)

if (!this.pendingCleanup) {
      return false;
    }
    for (const { renderTasks, operatorList } of this._intentStates.values()) {
      if (renderTasks.size > 0 || !operatorList.lastChunk) {
        return false;
      }
    }
    this._intentStates.clear();
    this.objs.clear();
    this._annotationsPromise = null;
    this._jsActionsPromise = null;
    this._xfaPromise = null;
    this._structTreePromise = null;
    if (resetStats && this._stats) {
      this._stats = new StatTimer();
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    this.pendingCleanup = false;
    return true;
  }
  /**
   * @private
   */
  _startRenderPage(transparency, intent) {