Link to PDF file (or attach file here):
https://issues.apache.org/jira/secure/attachment/12650283/000004_ShadingPatternTextPDF.pdf

Configuration:
- Web browser and its version: FF 51.0.1 32bit
- Operating system and its version: W7
- PDF.js version: latest

Steps to reproduce the problem:
display file

What is the expected behavior? (add screenshot)
![ok](https://cloud.githubusercontent.com/assets/6665575/23339534/5ff2de9c-fc25-11e6-837e-0fdaf81b4ca9.png)

What went wrong? (add screenshot)
![nok](https://cloud.githubusercontent.com/assets/6665575/23339536/63f7a37e-fc25-11e6-813c-cc218cc4def3.png)

possibly similar problem:
https://www.pdflib.com/fileadmin/pdflib/Cookbook/pdf/color_gradient.pdf (shaded text completely missing)
https://issues.apache.org/jira/secure/attachment/12630566/pslib-shading.pdf (page 4, part of text missing)
https://issues.apache.org/jira/secure/attachment/12652009/pattern-shading-2-4-idMatrix.pdf (some text missing)
https://issues.apache.org/jira/secure/attachment/12652010/pattern-shading-2-4-noMatrix.pdf (some text missing)

ctx.clip = function ctxRotate(rule) {
    destCtx.clip(rule);
    this.__originalClip(rule);
  };
  ctx.moveTo = function (x, y) {
    destCtx.moveTo(x, y);
    this.__originalMoveTo(x, y);
  };
  ctx.lineTo = function (x, y) {
    destCtx.lineTo(x, y);
    this.__originalLineTo(x, y);
  };
  ctx.bezierCurveTo = function (cp1x, cp1y, cp2x, cp2y, x, y) {
    destCtx.bezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);
    this.__originalBezierCurveTo(cp1x, cp1y, cp2x, cp2y, x, y);
  };
  ctx.rect = function (x, y, width, height) {
    destCtx.rect(x, y, width, height);
    this.__originalRect(x, y, width, height);
  };
  ctx.closePath = function () {
    destCtx.closePath();
    this.__originalClosePath();
  };
  ctx.beginPath = function () {
    destCtx.beginPath();
    this.__originalBeginPath();
  };
}
function addContextCurrentTransform(ctx) {