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):

this._transformMatrix = old.slice(0, 6);
    this._originalSave();
  };
  ctx.restore = function ctxRestore() {
    const prev = this._transformStack.pop();
    if (prev) {
      this._transformMatrix = prev;
      this._originalRestore();
    }
  };
  ctx.translate = function ctxTranslate(x, y) {
    const m = this._transformMatrix;
    m[4] = m[0] * x + m[2] * y + m[4];
    m[5] = m[1] * x + m[3] * y + m[5];
    this._originalTranslate(x, y);
  };
  ctx.scale = function ctxScale(x, y) {
    const m = this._transformMatrix;
    m[0] *= x;
    m[1] *= x;
    m[2] *= y;
    m[3] *= y;
    this._originalScale(x, y);
  };
  ctx.transform = function ctxTransform(a, b, c, d, e, f) {
    const m = this._transformMatrix;
    this._transformMatrix = [
      m[0] * a + m[2] * b,
      m[1] * a + m[3] * b,
      m[0] * c + m[2] * d,