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):

dimy.size,
      true
    );
    const tmpCtx = tmpCanvas.context;
    const graphics = canvasGraphicsFactory.createCanvasGraphics(tmpCtx);
    graphics.groupLevel = owner.groupLevel;
    this.setFillAndStrokeStyleToContext(graphics, paintType, color);
    let adjustedX0 = x0;
    let adjustedY0 = y0;
    let adjustedX1 = x1;
    let adjustedY1 = y1;
    
    
    
    if (x0 < 0) {
      adjustedX0 = 0;
      adjustedX1 += Math.abs(x0);
    }
    if (y0 < 0) {
      adjustedY0 = 0;
      adjustedY1 += Math.abs(y0);
    }
    tmpCtx.translate(-(dimx.scale * adjustedX0), -(dimy.scale * adjustedY0));
    graphics.transform(dimx.scale, 0, 0, dimy.scale, 0, 0);
    this.clipBbox(graphics, adjustedX0, adjustedY0, adjustedX1, adjustedY1);
    graphics.baseTransform = graphics.ctx.mozCurrentTransform.slice();
    graphics.executeOperatorList(operatorList);
    graphics.endDrawing();
    return {
      canvas: tmpCanvas.canvas,