Attach (recommended) or Link to PDF file here:
[shading_pattern.pdf](https://github.com/mozilla/pdf.js/files/1532598/shading_pattern.pdf)

Configuration:
- Web browser and its version: Firefox 57.0
- Operating system and its version: Debian GNU/Linux 9 64-bit
- PDF.js version: tried with Firefox's 1.9.583 and with online viewer 2.0.185
- Is a browser extension: no

Steps to reproduce the problem:
1. Open the attached file with the online viewer https://mozilla.github.io/pdf.js/web/viewer.html

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/11061462/33626267-d9a57dee-d9d8-11e7-8712-cfa17c038259.png)
(Image captured from Adobe Reader CS.) The shading needs to be inside the letters.

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/11061462/33626285-eaabd462-d9d8-11e7-94e2-96480b57750d.png)
The shading seems to be displaced and upside-down, for it does not cover all the characters of the word.

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):

maskCtx,
            this,
            ctx.mozCurrentTransformInverse,
            false
          )
        : fillColor;
      maskCtx.fillRect(0, 0, width, height);
      maskCtx.restore();
      ctx.save();
      ctx.transform.apply(ctx, image.transform);
      ctx.scale(1, -1);
      ctx.drawImage(maskCanvas.canvas, 0, 0, width, height, 0, -1, 1, 1);
      ctx.restore();
    }
    this.compose();
  }
  paintImageXObject(objId) {
    if (!this.contentVisible) {
      return;
    }
    const imgData = objId.startsWith("g_")
      ? this.commonObjs.get(objId)
      : this.objs.get(objId);
    if (!imgData) {
      warn("Dependent image isn't ready yet");
      return;
    }
    this.paintInlineImageXObject(imgData);
  }
  paintImageXObjectRepeat(objId, scaleX, scaleY, positions) {