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
inverse[0] * inverse[0] + inverse[1] * inverse[1],
            inverse[2] * inverse[2] + inverse[3] * inverse[3]
          )
        );
      }
      return this._cachedGetSinglePixelWidth;
    },
    getCanvasPosition: function CanvasGraphics_getCanvasPosition(x, y) {
      const transform = this.ctx.mozCurrentTransform;
      return [
        transform[0] * x + transform[2] * y + transform[4],
        transform[1] * x + transform[3] * y + transform[5],
      ];
    },
    isContentVisible: function CanvasGraphics_isContentVisible() {
      for (let i = this.markedContentStack.length - 1; i >= 0; i--) {
        if (!this.markedContentStack[i].visible) {
          return false;
        }
      }
      return true;
    },
  };
  for (const op in OPS) {
    CanvasGraphics.prototype[OPS[op]] = CanvasGraphics.prototype[op];
  }
  return CanvasGraphics;
})();
export { CanvasGraphics };