src/vs/workbench/contrib/terminal/browser/terminalGroup.ts/SplitPaneContainer/getPaneSize
class SplitPaneContainer:	getPaneSize(instance: ITerminalInstance): number {
		const paneForInstance = this._terminalToPane.get(instance);
		if (!paneForInstance) {
			return 0;
		}

		const index = this._children.indexOf(paneForInstance);
		return this._splitView.getViewSize(index);
	}