Merge "Move AlphaFilterCanvas to new API."

    AlphaFilterCanvas(SkCanvas* canvas, float alpha) : SkPaintFilterCanvas(canvas), mAlpha(alpha) {}

protected:

    bool onFilter(SkTCopyOnFirstWrite<SkPaint>* paint, Type t) const override {

        std::optional<SkPaint> defaultPaint;

        if (!*paint) {

            paint->init(defaultPaint.emplace());

        }

        paint->writable()->setAlpha((uint8_t)(*paint)->getAlpha() * mAlpha);

    bool onFilter(SkPaint& paint) const override {

        paint.setAlpha((uint8_t)paint.getAlpha() * mAlpha);

        return true;

    }

    void onDrawDrawable(SkDrawable* drawable, const SkMatrix* matrix) override {

        // We unroll the drawable using "this" canvas, so that draw calls contained inside will

        // get their alpha applied. THe default SkPaintFilterCanvas::onDrawDrawable does not unroll.

        // get their alpha applied. The default SkPaintFilterCanvas::onDrawDrawable does not unroll.

        drawable->draw(this, matrix);

    }