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

chrome/browser/resources/md_bookmarks/list.js

Index: chrome/browser/resources/md_bookmarks/list.js
diff --git a/chrome/browser/resources/md_bookmarks/list.js b/chrome/browser/resources/md_bookmarks/list.js
index f960e2eb5243cc862611af4093176d11d3436e3d..7ecac29cf3e2de20a4fd2f5f602cee24c6aeb38f 100644
--- a/chrome/browser/resources/md_bookmarks/list.js
+++ b/chrome/browser/resources/md_bookmarks/list.js
@@ -130,6 +130,7 @@ Polymer({
     var focusMoved = false;
     var focusedIndex =
         this.getIndexForItemElement_(/** @type {HTMLElement} */ (e.target));
+    var oldFocusedIndex = focusedIndex;
     if (e.key == 'ArrowUp') {
       focusedIndex--;
       focusMoved = true;
@@ -166,6 +167,12 @@ Polymer({
         this.dispatch(
             bookmarks.actions.updateAnchor(this.displayedIds_[focusedIndex]));
       } else {
+        // If shift-selecting with no anchor, use the old focus index.
+        if (e.shiftKey && this.getState().selection.anchor == null) {
+          this.dispatch(bookmarks.actions.updateAnchor(
+              this.displayedIds_[oldFocusedIndex]));
+        }
+
         // If the focus moved from something other than a Ctrl + move event,
         // update the selection.
         var config = {