src/vs/workbench/api/common/extHostCustomEditors.ts/EditorProviderStore/addCustomProvider
class EditorProviderStore:	public addCustomProvider(viewType: string, extension: IExtensionDescription, provider: vscode.CustomReadonlyEditorProvider): vscode.Disposable {
		return this.add(WebviewEditorType.Custom, viewType, extension, provider);
	}