Attach (recommended) or Link to PDF file here:
[298865.pdf](https://github.com/mozilla/pdf.js/files/2753236/298865.pdf)


Configuration:
- Web browser and its version:chrome 71.0.3578.98
- Operating system and its version:mac os 10.12.6
- PDF.js version:I use online demo in github
- Is a browser extension:no

Steps to reproduce the problem:
1. search "中华" or "电力" or so on,the highlight position is not right

What is the expected behavior? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087378-7eff5100-178d-11e9-991a-005d77b82f31.png)

What went wrong? (add screenshot)
![image](https://user-images.githubusercontent.com/10000986/51087374-6ee77180-178d-11e9-9707-281924f95fd0.png)

Link to a viewer (if hosted on a site other than mozilla.github.io/pdf.js or as Firefox/Chrome extension):
https://mozilla.github.io/pdf.js/web/viewer.html
const bounds = task._bounds;
  const viewport = task._viewport;
  const expanded = expandBounds(viewport.width, viewport.height, bounds);
  for (let i = 0; i < expanded.length; i++) {
    const div = bounds[i].div;
    const divProperties = task._textDivProperties.get(div);
    if (divProperties.angle === 0) {
      divProperties.paddingLeft = bounds[i].left - expanded[i].left;
      divProperties.paddingTop = bounds[i].top - expanded[i].top;
      divProperties.paddingRight = expanded[i].right - bounds[i].right;
      divProperties.paddingBottom = expanded[i].bottom - bounds[i].bottom;
      task._textDivProperties.set(div, divProperties);
      continue;
    }
    
    
    const e = expanded[i],
      b = bounds[i];
    const m = b.m,
      c = m[0],
      s = m[1];
    
    const points = [[0, 0], [0, b.size[1]], [b.size[0], 0], b.size];
    const ts = new Float64Array(64);