[MD Bookmarks] Make shift-selection behave well with no anchor.

chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js

Index: chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js
diff --git a/chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js b/chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js
index d7957ff70e118ea0c221e7f1ba0114d8f0fc6899..b60974e8d891cbabbb56c3afa67f293b6d4db61b 100644
--- a/chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js
+++ b/chrome/test/data/webui/md_bookmarks/md_bookmarks_focus_test.js
@@ -265,14 +265,16 @@ TEST_F('MaterialBookmarksFocusTest', 'All', function() {
     });
 
     test('shift selection', function() {
-      // TODO(calamity): Make the first item the anchor index when a new folder
-      // is selected.
       var focusedItem = items[0];
       focusedItem.focus();
 
-      keydown(focusedItem, 'ArrowDown');
+      keydown(focusedItem, 'ArrowDown', 'shift');
       focusedItem = items[1];
-      assertDeepEquals(['3'], normalizeSet(store.data.selection.items));
+      assertDeepEquals(['2', '3'], normalizeSet(store.data.selection.items));
+
+      keydown(focusedItem, 'Escape');
+      focusedItem = items[1];
+      assertDeepEquals([], normalizeSet(store.data.selection.items));
 
       keydown(focusedItem, 'ArrowUp', 'shift');
       focusedItem = items[0];