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
endMarkedContent: function CanvasGraphics_endMarkedContent() {
      this.markedContentStack.pop();
      this.contentVisible = this.isContentVisible();
    },
    
    beginCompat: function CanvasGraphics_beginCompat() {
      
    },
    endCompat: function CanvasGraphics_endCompat() {
      
    },
    
    consumePath: function CanvasGraphics_consumePath() {
      const ctx = this.ctx;
      if (this.pendingClip) {
        if (this.pendingClip === EO_CLIP) {
          ctx.clip("evenodd");
        } else {
          ctx.clip();
        }
        this.pendingClip = null;
      }
      ctx.beginPath();
    },
    getSinglePixelWidth(scale) {
      if (this._cachedGetSinglePixelWidth === null) {
        const inverse = this.ctx.mozCurrentTransformInverse;
        
        this._cachedGetSinglePixelWidth = Math.sqrt(
          Math.max(