src/vs/workbench/api/browser/mainThreadWebviewPanels.ts/MainThreadWebviewPanels/getWebviewInput
class MainThreadWebviewPanels:	private getWebviewInput(handle: extHostProtocol.WebviewHandle): WebviewInput {
		const webview = this.tryGetWebviewInput(handle);
		if (!webview) {
			throw new Error(`Unknown webview handle:${handle}`);
		}
		return webview;
	}