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):

if (ctx.mozCurrentTransform) {
    return;
  }
  ctx._originalSave = ctx.save;
  ctx._originalRestore = ctx.restore;
  ctx._originalRotate = ctx.rotate;
  ctx._originalScale = ctx.scale;
  ctx._originalTranslate = ctx.translate;
  ctx._originalTransform = ctx.transform;
  ctx._originalSetTransform = ctx.setTransform;
  ctx._originalResetTransform = ctx.resetTransform;
  ctx._transformMatrix = ctx._transformMatrix || [1, 0, 0, 1, 0, 0];
  ctx._transformStack = [];
  try {
    
    
    
    const desc = Object.getOwnPropertyDescriptor(
      Object.getPrototypeOf(ctx),
      "lineWidth"
    );
    ctx._setLineWidth = desc.set;
    ctx._getLineWidth = desc.get;
    Object.defineProperty(ctx, "lineWidth", {
      set: function setLineWidth(width) {
        this._setLineWidth(width * LINEWIDTH_SCALE_FACTOR);
      },
      get: function getLineWidth() {