Attach (recommended) or Link to PDF file here:
https://drive.google.com/open?id=1UjLxnFw2g3gn3tvNLRYLdmG6mFdFKCcr

Configuration:
- Web browser and its version: Chrome 77.0.3865.90
- Operating system and its version: Mac mojave 10.14.6
- PDF.js version: 2.3.194
- Is a browser extension: Nope

Steps to reproduce the problem:
1. Make sure to set `renderInteractiveForms` to `true`
2. The read-only form field(Sample title) doesn't honor it's proper font-size

What is the expected behavior?
<img width="862" alt="write" src="https://user-images.githubusercontent.com/4616548/66152094-4a009a80-e64b-11e9-81dc-178068055efa.png">

What went wrong?
<img width="842" alt="wrong" src="https://user-images.githubusercontent.com/4616548/66152100-4d942180-e64b-11e9-91a8-ad9caf451f98.png">


line = font.encodeString(line).join("");
    const glyphs = font.charsToGlyphs(line);
    if (glyphs.length <= 1) {
      
      return [line];
    }
    const positions = font.getCharPositions(line);
    const scale = fontSize / 1000;
    const chunks = [];
    let lastSpacePosInStringStart = -1,
      lastSpacePosInStringEnd = -1,
      lastSpacePos = -1,
      startChunk = 0,
      currentWidth = 0;
    for (let i = 0, ii = glyphs.length; i < ii; i++) {
      const [start, end] = positions[i];
      const glyph = glyphs[i];
      const glyphWidth = glyph.width * scale;
      if (glyph.unicode === " ") {
        if (currentWidth + glyphWidth > width) {
          
          chunks.push(line.substring(startChunk, start));
          startChunk = start;
          currentWidth = glyphWidth;
          lastSpacePosInStringStart = -1;
          lastSpacePos = -1;
        } else {
          currentWidth += glyphWidth;