src/vs/workbench/api/browser/mainThreadWebviewViews.ts/MainThreadWebviewsViews/getWebviewView
class MainThreadWebviewsViews:	private getWebviewView(handle: string): WebviewView {
		const webviewView = this._webviewViews.get(handle);
		if (!webviewView) {
			throw new Error('unknown webview view');
		}
		return webviewView;
	}