src/vs/workbench/contrib/terminal/browser/terminalService.ts/TerminalService/_forwardInstanceHostEvents
class TerminalService:	private _forwardInstanceHostEvents(host: ITerminalInstanceHost) {
		host.onDidChangeInstances(this._onDidChangeInstances.fire, this._onDidChangeInstances);
		host.onDidDisposeInstance(this._onDidDisposeInstance.fire, this._onDidDisposeInstance);
		host.onDidChangeActiveInstance(instance => this._evaluateActiveInstance(host, instance));
		host.onDidFocusInstance(instance => {
			this._onDidFocusInstance.fire(instance);
			this._evaluateActiveInstance(host, instance);
		});
		this._hostActiveTerminals.set(host, undefined);
	}