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)

let canvasEntry;
    if (this.cache[id] !== undefined) {
      canvasEntry = this.cache[id];
      this.canvasFactory.reset(canvasEntry, width, height);
      
      canvasEntry.context.setTransform(1, 0, 0, 1, 0, 0);
    } else {
      canvasEntry = this.canvasFactory.create(width, height);
      this.cache[id] = canvasEntry;
    }
    if (trackTransform) {
      addContextCurrentTransform(canvasEntry.context);
    }
    return canvasEntry;
  }
  clear() {
    for (const id in this.cache) {
      const canvasEntry = this.cache[id];
      this.canvasFactory.destroy(canvasEntry);
      delete this.cache[id];
    }
  }
}
/**
 * Least recently used cache implemented with a JS Map. JS Map keys are ordered
 * by last insertion.
 */
class LRUCache {