WebUI: Close cr-action-menu on popstate event.

chrome/test/data/webui/cr_elements/cr_action_menu_test.js

Index: chrome/test/data/webui/cr_elements/cr_action_menu_test.js
diff --git a/chrome/test/data/webui/cr_elements/cr_action_menu_test.js b/chrome/test/data/webui/cr_elements/cr_action_menu_test.js
index 6cfa650138258af262bf93a50f68d6d88208bec0..15dd8e0da2cc483f4da159d6918634e5d4040342 100644
--- a/chrome/test/data/webui/cr_elements/cr_action_menu_test.js
+++ b/chrome/test/data/webui/cr_elements/cr_action_menu_test.js
@@ -96,6 +96,14 @@ suite('CrActionMenu', function() {
     assertFalse(menu.open);
   });
 
+  test('close on popstate', function() {
+    menu.showAt(document.querySelector('#dots'));
+    assertTrue(menu.open);
+
+    window.dispatchEvent(new CustomEvent('popstate'));
+    assertFalse(menu.open);
+  });
+
   /** @param {string} key The key to use for closing. */
   function testFocusAfterClosing(key) {
     return new Promise(function(resolve) {