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
color,
          this.ctx,
          canvasGraphicsFactory,
          baseTransform
        );
      } else {
        pattern = getShadingPatternFromIR(IR);
      }
      return pattern;
    },
    setStrokeColorN: function CanvasGraphics_setStrokeColorN() {
      this.current.strokeColor = this.getColorN_Pattern(arguments);
    },
    setFillColorN: function CanvasGraphics_setFillColorN() {
      this.current.fillColor = this.getColorN_Pattern(arguments);
      this.current.patternFill = true;
    },
    setStrokeRGBColor: function CanvasGraphics_setStrokeRGBColor(r, g, b) {
      const color = Util.makeHexColor(r, g, b);
      this.ctx.strokeStyle = color;
      this.current.strokeColor = color;
    },
    setFillRGBColor: function CanvasGraphics_setFillRGBColor(r, g, b) {
      const color = Util.makeHexColor(r, g, b);
      this.ctx.fillStyle = color;
      this.current.fillColor = color;
      this.current.patternFill = false;
    },
    shadingFill: function CanvasGraphics_shadingFill(patternIR) {
      if (!this.contentVisible) {