src/vs/workbench/api/common/extHostWindow.ts/ExtHostWindow/constructor
class ExtHostWindow:	constructor(@IExtHostRpcService extHostRpc: IExtHostRpcService) {
		this._proxy = extHostRpc.getProxy(MainContext.MainThreadWindow);
		this._proxy.$getWindowVisibility().then(isFocused => this.$onDidChangeWindowFocus(isFocused));
	}