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):

scaleX: dimx.scale,
      scaleY: dimy.scale,
      offsetX: adjustedX0,
      offsetY: adjustedY0,
    };
  }
  getSizeAndScale(step, realOutputSize, scale) {
    
    step = Math.abs(step);
    
    
    
    
    const maxSize = Math.max(TilingPattern.MAX_PATTERN_SIZE, realOutputSize);
    let size = Math.ceil(step * scale);
    if (size >= maxSize) {
      size = maxSize;
    } else {
      scale = size / step;
    }
    return { scale, size };
  }
  clipBbox(graphics, x0, y0, x1, y1) {
    const bboxWidth = x1 - x0;
    const bboxHeight = y1 - y0;
    graphics.ctx.rect(x0, y0, bboxWidth, bboxHeight);
    graphics.clip();
    graphics.endPath();
  }
  setFillAndStrokeStyleToContext(graphics, paintType, color) {