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 characterScaleX = width / measuredWidth;
          restoreNeeded = true;
          ctx.save();
          ctx.scale(characterScaleX, 1);
          scaledX /= characterScaleX;
        } else if (width !== measuredWidth) {
          scaledX +=
            (((width - measuredWidth) / 2000) * fontSize) / fontSizeScale;
        }
      }
      
      
      if (this.contentVisible && (glyph.isInFont || font.missingFile)) {
        if (simpleFillText && !accent) {
          
          ctx.fillText(character, scaledX, scaledY);
        } else {
          this.paintChar(
            character,
            scaledX,
            scaledY,
            patternTransform,
            resetLineWidthToOne
          );
          if (accent) {
            const scaledAccentX =
              scaledX + (fontSize * accent.offset.x) / fontSizeScale;
            const scaledAccentY =
              scaledY - (fontSize * accent.offset.y) / fontSizeScale;
            this.paintChar(