Bug 1659259 - Don't reconstruct frames as a result of font-list refresh if...

      mMissingFonts = nullptr;

    }

  }

  if (prefName.EqualsLiteral("font.internaluseonly.changed")) {

  if (prefName.EqualsLiteral("font.internaluseonly.changed") &&

      !IsPrintingOrPrintPreview()) {

    // If there's a change to the font list, we generally need to reconstruct

    // frames, as the existing frames may be referring to fonts that are no

    // longer available. But in the case of a static-clone document used for

    // printing or print-preview, this is undesirable because the nsPrintJob

    // is holding weak refs to frames that will get blown away unexpectedly by

    // this reconstruction. So the prescontext for a print/preview doc ignores

    // the font-list update.

    //

    // This means the print document may still be using cached fonts that are

    // no longer present in the font list, but that should be safe given that

    // all the required font instances have already been created, so it won't

    // be depending on access to the font-list entries.

    //

    // XXX Actually, I think it's probably a bad idea to do *any* restyling of

    // print documents in response to pref changes. We could be in the middle

    // of printing the document, and reflowing all the frames might cause some

    // kind of unwanted mid-document discontinuity.

    mChangeHintForPrefChange |= nsChangeHint_ReconstructFrame;

  } else if (StringBeginsWith(prefName, "font."_ns) ||

             // Changes to font family preferences don't change anything in the