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
}
      this.ctx.fillRect(0, 0, 1, 1);
    },
    
    markPoint: function CanvasGraphics_markPoint(tag) {
      
    },
    markPointProps: function CanvasGraphics_markPointProps(tag, properties) {
      
    },
    beginMarkedContent: function CanvasGraphics_beginMarkedContent(tag) {
      this.markedContentStack.push({
        visible: true,
      });
    },
    beginMarkedContentProps: function CanvasGraphics_beginMarkedContentProps(
      tag,
      properties
    ) {
      if (tag === "OC") {
        this.markedContentStack.push({
          visible: this.optionalContentConfig.isVisible(properties),
        });
      } else {
        this.markedContentStack.push({
          visible: true,
        });
      }
      this.contentVisible = this.isContentVisible();
    },