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):

);
    const tmpCtx = tmpCanvas.context;
    const data = tmpCtx.createImageData(width, height);
    if (backgroundColor) {
      const bytes = data.data;
      for (let i = 0, ii = bytes.length; i < ii; i += 4) {
        bytes[i] = backgroundColor[0];
        bytes[i + 1] = backgroundColor[1];
        bytes[i + 2] = backgroundColor[2];
        bytes[i + 3] = 255;
      }
    }
    for (const figure of this._figures) {
      drawFigure(data, figure, context);
    }
    tmpCtx.putImageData(data, BORDER_SIZE, BORDER_SIZE);
    const canvas = tmpCanvas.canvas;
    return {
      canvas,
      offsetX: offsetX - BORDER_SIZE * scaleX,
      offsetY: offsetY - BORDER_SIZE * scaleY,
      scaleX,
      scaleY,
    };
  }
  getPattern(ctx, owner, inverse, shadingFill = false) {
    applyBoundingBox(ctx, this._bbox);
    let scale;
    if (shadingFill) {
      scale = Util.singularValueDecompose2dScale(ctx.mozCurrentTransform);