Fix lint.

Author: William Chou

extensions/amp-list/0.1/amp-list.js

@@ -52,6 +52,7 @@ import {dict, getValueForExpr} from '../../../src/core/types/object';
 import {getMode} from '../../../src/mode';
 import {getSourceOrigin, isAmpScriptUri} from '../../../src/url';
 
+import {escapeCssSelectorIdent} from '../../../src/core/dom/css';
 import {isAmp4Email} from '../../../src/format';
 import {isArray, toArray} from '../../../src/core/types/array';
 import {isExperimentOn} from '../../../src/experiments';
@@ -322,12 +323,12 @@ export class AmpList extends AMP.BaseElement {
   /**
    * A "diffable placeholder" is the child container <div> (which is usually created by the amp-list
    * to hold the rendered children). It serves the same purpose as a placeholder, except it can be diffed.
-   * 
+   *
    * For example:
    * <amp-list>
    *   <div placeholder>I'm displayed before render.</div>
    * </amp-list>
-   * 
+   *
    * <amp-list diffable>
    *   <div role=list>I'm displayed before render.</div>
    * </amp-list>
@@ -336,11 +337,16 @@ export class AmpList extends AMP.BaseElement {
    * @private
    */
   queryDiffablePlaceholder_() {
-    const roleSelector = this.element.hasAttribute('single-item') ? '' : '[role=list]'
+    const roleSelector = this.element.hasAttribute('single-item')
+      ? ''
+      : '[role=list]';
+
     return scopedQuerySelector(
       this.element,
       // Don't select other special <div> children used for placeholders/fallback/etc.
-      `> div${roleSelector}:not([placeholder]):not([fallback]):not([fetch-error])`
+      `> div${escapeCssSelectorIdent(
+        roleSelector
+      )}:not([placeholder]):not([fallback]):not([fetch-error])`
     );
   }