src/vs/editor/browser/viewParts/lines/viewLines.ts/ViewLines/_checkMonospaceFontAssumptions
class ViewLines:	private _checkMonospaceFontAssumptions(): void {
		// Problems with monospace assumptions are more apparent for longer lines,
		// as small rounding errors start to sum up, so we will select the longest
		// line for a closer inspection
		let longestLineNumber = -1;
		let longestWidth = -1;
		const rendStartLineNumber = this._visibleLines.getStartLineNumber();
		const rendEndLineNumber = this._visibleLines.getEndLineNumber();
		for (let lineNumber = rendStartLineNumber; lineNumber <= rendEndLineNumber; lineNumber++) {
			const visibleLine = this._visibleLines.getVisibleLine(lineNumber);
			if (visibleLine.needsMonospaceFontCheck()) {
				const lineWidth = visibleLine.getWidth();
				if (lineWidth > longestWidth) {
					longestWidth = lineWidth;
					longestLineNumber = lineNumber;
				}
			}
		}

		if (longestLineNumber === -1) {
			return;
		}

		if (!this._visibleLines.getVisibleLine(longestLineNumber).monospaceAssumptionsAreValid()) {
			for (let lineNumber = rendStartLineNumber; lineNumber <= rendEndLineNumber; lineNumber++) {
				const visibleLine = this._visibleLines.getVisibleLine(lineNumber);
				visibleLine.onMonospaceAssumptionsInvalidated();
			}
		}
	}