Prevent Meta Info from being overwritten due to reordering of entries.

chrome/browser/sync/glue/bookmark_change_processor.cc

Index: chrome/browser/sync/glue/bookmark_change_processor.cc
diff --git a/chrome/browser/sync/glue/bookmark_change_processor.cc b/chrome/browser/sync/glue/bookmark_change_processor.cc
index 430843d95eab4d50ba8be7e103c9ca4b03081f12..ce9ae91de18d85b762da2e7d1434b3645969fca8 100644
--- a/chrome/browser/sync/glue/bookmark_change_processor.cc
+++ b/chrome/browser/sync/glue/bookmark_change_processor.cc
@@ -845,6 +845,9 @@ BookmarkChangeProcessor::GetBookmarkMetaInfo(
     (*meta_info_map)[specifics.meta_info(i).key()] =
         specifics.meta_info(i).value();
   }
+  // Verifies that all entries had unique keys.
+  DCHECK_EQ(static_cast<size_t>(specifics.meta_info_size()),
+            meta_info_map->size());
   return meta_info_map.Pass();
 }
 
@@ -853,8 +856,34 @@ void BookmarkChangeProcessor::SetSyncNodeMetaInfo(
     const BookmarkNode* node,
     syncer::WriteNode* sync_node) {
   sync_pb::BookmarkSpecifics specifics = sync_node->GetBookmarkSpecifics();
-  specifics.clear_meta_info();
   const BookmarkNode::MetaInfoMap* meta_info_map = node->GetMetaInfoMap();
+
+  // Compare specifics meta info to node meta info before making the change.
+  // Please note that the original specifics meta info is unordered while
+  //  meta_info_map is ordered by key. Setting the meta info blindly into
+  // the specifics might cause an unnecessary change.
+  size_t size = meta_info_map ? meta_info_map->size() : 0;
+  if (static_cast<size_t>(specifics.meta_info_size()) == size) {
+    size_t index = 0;
+    for (; index < size; index++) {
+      const sync_pb::MetaInfo& meta_info = specifics.meta_info(index);
+      BookmarkNode::MetaInfoMap::const_iterator it =
+          meta_info_map->find(meta_info.key());
+      if (it == meta_info_map->end() || it->second != meta_info.value()) {
+        // One of original meta info entries is missing in |meta_info_map| or
+        // different.
+        break;
+      }
+    }
+    if (index == size) {
+      // The original meta info from the sync model is already equivalent to
+      // |meta_info_map|.
+      return;
+    }
+  }
+
+  // Clear and reset meta info in bookmark specifics.
+  specifics.clear_meta_info();
   if (meta_info_map) {
     for (BookmarkNode::MetaInfoMap::const_iterator it = meta_info_map->begin();
         it != meta_info_map->end(); ++it) {
@@ -863,6 +892,7 @@ void BookmarkChangeProcessor::SetSyncNodeMetaInfo(
       meta_info->set_value(it->second);
     }
   }
+
   sync_node->SetBookmarkSpecifics(specifics);
 }