[Sync::USS] Implement OnWillRemoveAllUserBookmarks for USS

Bug: 516866
Change-Id: I38696ce73cf0ab206997401a8a88c182b319be5c
Reviewed-on: https://chromium-review.googlesource.com/1190244
Commit-Queue: Mohamed Amir Yosef <mamir@chromium.org>
Reviewed-by: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588383}

chrome/browser/sync/test/integration/two_client_bookmarks_sync_test.cc

@@ -2002,7 +2002,7 @@ IN_PROC_BROWSER_TEST_P(TwoClientBookmarksSyncTestIncludingUssTests,
   ASSERT_TRUE(BookmarksMatchChecker().Wait());
 }
 
-IN_PROC_BROWSER_TEST_F(TwoClientBookmarksSyncTest,
+IN_PROC_BROWSER_TEST_P(TwoClientBookmarksSyncTestIncludingUssTests,
                        BookmarkAllNodesRemovedEvent) {
   ASSERT_TRUE(SetupSync()) << "SetupSync() failed.";
   ASSERT_TRUE(AllModelsMatchVerifier());

components/sync_bookmarks/bookmark_model_observer_impl.cc

@@ -129,10 +129,25 @@ void BookmarkModelObserverImpl::BookmarkNodeRemoved(
   DCHECK(bookmark_tracker_->GetEntityForBookmarkNode(node) == nullptr);
 }
 
+void BookmarkModelObserverImpl::OnWillRemoveAllUserBookmarks(
+    bookmarks::BookmarkModel* model) {
+  const bookmarks::BookmarkNode* root_node = model->root_node();
+  for (int i = 0; i < root_node->child_count(); ++i) {
+    const bookmarks::BookmarkNode* permanent_node = root_node->GetChild(i);
+    for (int j = permanent_node->child_count() - 1; j >= 0; --j) {
+      if (!model->client()->CanSyncNode(permanent_node->GetChild(j))) {
+        continue;
+      }
+      ProcessDelete(permanent_node, permanent_node->GetChild(j));
+    }
+  }
+  nudge_for_commit_closure_.Run();
+}
+
 void BookmarkModelObserverImpl::BookmarkAllUserNodesRemoved(
     bookmarks::BookmarkModel* model,
     const std::set<GURL>& removed_urls) {
-  NOTIMPLEMENTED();
+  // All the work should have already been done in OnWillRemoveAllUserBookmarks.
 }
 
 void BookmarkModelObserverImpl::BookmarkNodeChanged(

components/sync_bookmarks/bookmark_model_observer_impl.h

@@ -53,6 +53,7 @@ class BookmarkModelObserverImpl : public bookmarks::BookmarkModelObserver {
                            int old_index,
                            const bookmarks::BookmarkNode* node,
                            const std::set<GURL>& removed_urls) override;
+  void OnWillRemoveAllUserBookmarks(bookmarks::BookmarkModel* model) override;
   void BookmarkAllUserNodesRemoved(bookmarks::BookmarkModel* model,
                                    const std::set<GURL>& removed_urls) override;
   void BookmarkNodeChanged(bookmarks::BookmarkModel* model,