src/vs/workbench/api/browser/mainThreadUrls.ts/MainThreadUrls/$registerUriHandler
class MainThreadUrls:	$registerUriHandler(handle: number, extensionId: ExtensionIdentifier): Promise<void> {
		const handler = new ExtensionUrlHandler(this.proxy, handle, extensionId);
		const disposable = this.urlService.registerHandler(handler);

		this.handlers.set(handle, { extensionId, disposable });
		this.extensionUrlHandler.registerExtensionHandler(extensionId, handler);

		return Promise.resolve(undefined);
	}