extensions/markdown-language-features/src/preview/documentRenderer.ts/MdDocumentRenderer/_extensionResourcePath
class MdDocumentRenderer:	private _extensionResourcePath(resourceProvider: WebviewResourceProvider, mediaFile: string): string {
		const webviewResource = resourceProvider.asWebviewUri(
			vscode.Uri.joinPath(this._context.extensionUri, 'media', mediaFile));
		return webviewResource.toString();
	}