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):

}
    }
    ctx.putImageData(chunkImgData, 0, i * FULL_CHUNK_HEIGHT);
  }
}
function copyCtxState(sourceCtx, destCtx) {
  const properties = [
    "strokeStyle",
    "fillStyle",
    "fillRule",
    "globalAlpha",
    "lineWidth",
    "lineCap",
    "lineJoin",
    "miterLimit",
    "globalCompositeOperation",
    "font",
  ];
  for (let i = 0, ii = properties.length; i < ii; i++) {
    const property = properties[i];
    if (sourceCtx[property] !== undefined) {
      destCtx[property] = sourceCtx[property];
    }
  }
  if (sourceCtx.setLineDash !== undefined) {
    destCtx.setLineDash(sourceCtx.getLineDash());
    destCtx.lineDashOffset = sourceCtx.lineDashOffset;
  }
}
function resetCtxToDefault(ctx) {