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)

scaleX: dimx.scale,
      scaleY: dimy.scale,
      offsetX: adjustedX0,
      offsetY: adjustedY0,
    };
  }
  getSizeAndScale(step, realOutputSize, scale) {
    
    step = Math.abs(step);
    
    
    
    
    const maxSize = Math.max(TilingPattern.MAX_PATTERN_SIZE, realOutputSize);
    let size = Math.ceil(step * scale);
    if (size >= maxSize) {
      size = maxSize;
    } else {
      scale = size / step;
    }
    return { scale, size };
  }
  clipBbox(graphics, x0, y0, x1, y1) {
    const bboxWidth = x1 - x0;
    const bboxHeight = y1 - y0;
    graphics.ctx.rect(x0, y0, bboxWidth, bboxHeight);
    graphics.clip();
    graphics.endPath();
  }
  setFillAndStrokeStyleToContext(graphics, paintType, color) {