src/vs/platform/theme/common/iconRegistry.ts/IconRegistry/registerIconFont
class IconRegistry:	public registerIconFont(id: string, definition: IconFontDefinition): IconFontDefinition {
		const existing = this.iconFontsById[id];
		if (existing) {
			return existing;
		}
		this.iconFontsById[id] = definition;
		this._onDidChange.fire();
		return definition;
	}