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 pattern;
    if (IR[0] === "TilingPattern") {
      const color = IR[1];
      const baseTransform =
        this.baseTransform || this.ctx.mozCurrentTransform.slice();
      const canvasGraphicsFactory = {
        createCanvasGraphics: ctx => {
          return new CanvasGraphics(
            ctx,
            this.commonObjs,
            this.objs,
            this.canvasFactory
          );
        },
      };
      pattern = new TilingPattern(
        IR,
        color,
        this.ctx,
        canvasGraphicsFactory,
        baseTransform
      );
    } else {
      pattern = this._getPattern(IR[1], IR[2]);
    }
    return pattern;
  }
  setStrokeColorN() {