Add 2 egtests for the new iOS bookmarks

2 egtest2 are added:
1. testWhenCurrentFolderDeletedInBackground: test when the navigating
   folder of Bookmarks is deleted in background, empty background is
   shown with context bar buttons disabled.
2. testBookmarksURLDisabled: test chrome://bookmarks is disabled.

Bug: 782551
Change-Id: I1e0f4cc4960aca3094e673e812d040ec231d497c
Reviewed-on: https://chromium-review.googlesource.com/807410Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Marti Wong <martiw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521921}

ios/chrome/browser/ui/bookmarks/bookmark_home_view_controller.mm

@@ -962,6 +962,11 @@ std::vector<GURL> GetUrlsToOpen(const std::vector<const BookmarkNode*>& nodes) {
 - (void)bookmarkNodeDeleted:(const BookmarkNode*)node
                  fromFolder:(const BookmarkNode*)folder {
   [self removeEditNode:node atIndexPath:nil];
+
+  if (_rootNode == node &&
+      base::FeatureList::IsEnabled(kBookmarkNewGeneration)) {
+    [self setTableViewEditing:NO];
+  }
 }
 
 - (void)bookmarkModelRemovedAllNodes {

ios/chrome/browser/ui/bookmarks/bookmark_table_view.mm

@@ -697,12 +697,13 @@ using IntegerPair = std::pair<NSInteger, NSInteger>;
 
 // Computes the bookmarks table view based on the current root node.
 - (void)computeBookmarkTableViewData {
+  // Regenerate the list of all bookmarks.
+  _bookmarkItems.clear();
+
   if (!self.bookmarkModel->loaded() || !_currentRootNode) {
     return;
   }
 
-  // Regenerate the list of all bookmarks.
-  _bookmarkItems.clear();
   if (_currentRootNode == self.bookmarkModel->root_node()) {
     [self generateTableViewDataForRootNode];
     return;