src/vs/workbench/contrib/webviewView/browser/webviewViewService.ts/WebviewViewService/register
class WebviewViewService:	register(viewType: string, resolver: IWebviewViewResolver): IDisposable {
		if (this._resolvers.has(viewType)) {
			throw new Error(`View resolver already registered for ${viewType}`);
		}

		this._resolvers.set(viewType, resolver);
		this._onNewResolverRegistered.fire({ viewType: viewType });

		const pending = this._awaitingRevival.get(viewType);
		if (pending) {
			resolver.resolve(pending.webview, CancellationToken.None).then(() => {
				this._awaitingRevival.delete(viewType);
				pending.resolve();
			});
		}

		return toDisposable(() => {
			this._resolvers.delete(viewType);
		});
	}