src/vs/editor/browser/viewParts/lines/viewLine.ts/FastRenderedViewLine/monospaceAssumptionsAreValid
class FastRenderedViewLine:	public monospaceAssumptionsAreValid(): boolean {
		if (!this.domNode) {
			return monospaceAssumptionsAreValid;
		}
		const expectedWidth = this.getWidth();
		const actualWidth = (<HTMLSpanElement>this.domNode.domNode.firstChild).offsetWidth;
		if (Math.abs(expectedWidth - actualWidth) >= 2) {
			// more than 2px off
			console.warn(`monospace assumptions have been violated, therefore disabling monospace optimizations!`);
			monospaceAssumptionsAreValid = false;
		}
		return monospaceAssumptionsAreValid;
	}