Adopt unordered containers for bookmark sync

Some users have a huge amount of bookmarks (>100K) and ordered STL
containers can run into performance issues.

To reduce UI jank during browser startup, let's trivially adopt
unordered containers. This can help reduce the time spent in
SyncedBookmarkTracker::InitEntitiesFromModelAndMetadata().

Change-Id: Id789a1d8f0aa14a94aa0974b939568b966be6300
Bug: 1068378
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2306253
Auto-Submit: Mikel Astiz <mastiz@chromium.org>
Reviewed-by: Marc Treib <treib@chromium.org>
Commit-Queue: Mikel Astiz <mastiz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#789917}

components/sync_bookmarks/synced_bookmark_tracker.cc

@@ -5,7 +5,6 @@
 #include "components/sync_bookmarks/synced_bookmark_tracker.h"
 
 #include <algorithm>
-#include <set>
 #include <unordered_map>
 #include <unordered_set>
 
@@ -708,7 +707,7 @@ SyncedBookmarkTracker::ReorderUnsyncedEntitiesExceptDeletions(
   //    node. What's left in |nodes| are the roots of the forest.
   // 3. Start at each root in |nodes|, emit the update and recurse over its
   //    children.
-  std::set<const bookmarks::BookmarkNode*> nodes;
+  std::unordered_set<const bookmarks::BookmarkNode*> nodes;
   // Collect nodes with updates
   for (const SyncedBookmarkTracker::Entity* entity : entities) {
     DCHECK(entity->IsUnsynced());

components/sync_bookmarks/synced_bookmark_tracker.h

@@ -5,7 +5,6 @@
 #ifndef COMPONENTS_SYNC_BOOKMARKS_SYNCED_BOOKMARK_TRACKER_H_
 #define COMPONENTS_SYNC_BOOKMARKS_SYNCED_BOOKMARK_TRACKER_H_
 
-#include <map>
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ -351,7 +350,8 @@ class SyncedBookmarkTracker {
 
   // A map of sync server ids to sync entities. This should contain entries and
   // metadata for almost everything.
-  std::map<std::string, std::unique_ptr<Entity>> sync_id_to_entities_map_;
+  std::unordered_map<std::string, std::unique_ptr<Entity>>
+      sync_id_to_entities_map_;
 
   // A map of bookmark nodes to sync entities. It's keyed by the bookmark node
   // pointers which get assigned when loading the bookmark model. This map is