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
},
    
    clip: function CanvasGraphics_clip() {
      this.pendingClip = NORMAL_CLIP;
    },
    eoClip: function CanvasGraphics_eoClip() {
      this.pendingClip = EO_CLIP;
    },
    
    beginText: function CanvasGraphics_beginText() {
      this.current.textMatrix = IDENTITY_MATRIX;
      this.current.textMatrixScale = 1;
      this.current.x = this.current.lineX = 0;
      this.current.y = this.current.lineY = 0;
    },
    endText: function CanvasGraphics_endText() {
      const paths = this.pendingTextPaths;
      const ctx = this.ctx;
      if (paths === undefined) {
        ctx.beginPath();
        return;
      }
      ctx.save();
      ctx.beginPath();
      for (let i = 0; i < paths.length; i++) {
        const path = paths[i];
        ctx.setTransform.apply(ctx, path.transform);
        ctx.translate(path.x, path.y);
        path.addToPath(ctx, path.fontSize);
      }