src/vs/workbench/contrib/terminal/browser/terminalGroup.ts/SplitPaneContainer/getRelativePaneSize
class SplitPaneContainer:	getRelativePaneSize(instance: ITerminalInstance): number {
		const paneForInstance = this._terminalToPane.get(instance);
		if (!paneForInstance) {
			return 0;
		}
		return ((this.orientation === Orientation.HORIZONTAL ? paneForInstance.element.clientWidth : paneForInstance.element.clientHeight) / (this.orientation === Orientation.HORIZONTAL ? this._width : this._height));
	}