Steps to reproduce the problem:
1. When using the demo application - https://mozilla.github.io/pdf.js/web/viewer.html, load  the document 5311693-1.pdf

[5311693-1.pdf](https://github.com/mozilla/pdf.js/files/5137225/5311693-1.pdf)

2. go to Page 16 of the document.

3.  The strip of  EKG data  appears to have an incorrect line width   under the  Multi-color heat rate chart.

4.  When the same document is generated by pdffactory ,  the artifact are not visible.

What is the expected behavior? (add screenshot)
![expected](https://user-images.githubusercontent.com/3577617/91461157-4622cb80-e84e-11ea-8e5d-750c7b4e64ae.PNG)

What went wrong? (add screenshot)
The EKG line strip  has an incorrect thickness.  the x-transform seems to stretch the line thickness.  See the  stri in the RED rectagngle of the attached behavior versus the GREEN rectangle

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
}
      }
      ctx.putImageData(chunkImgData, 0, i * FULL_CHUNK_HEIGHT);
    }
  }
  function copyCtxState(sourceCtx, destCtx) {
    const properties = [
      "strokeStyle",
      "fillStyle",
      "fillRule",
      "globalAlpha",
      "lineWidth",
      "lineCap",
      "lineJoin",
      "miterLimit",
      "globalCompositeOperation",
      "font",
    ];
    for (let i = 0, ii = properties.length; i < ii; i++) {
      const property = properties[i];
      if (sourceCtx[property] !== undefined) {
        destCtx[property] = sourceCtx[property];
      }
    }
    if (sourceCtx.setLineDash !== undefined) {
      destCtx.setLineDash(sourceCtx.getLineDash());
      destCtx.lineDashOffset = sourceCtx.lineDashOffset;
    }
  }
  function resetCtxToDefault(ctx) {