[Sync] Don't commit items with predecessors/parents in conflict.

chrome/browser/sync/sessions/ordered_commit_set.cc

Index: chrome/browser/sync/sessions/ordered_commit_set.cc
diff --git a/chrome/browser/sync/sessions/ordered_commit_set.cc b/chrome/browser/sync/sessions/ordered_commit_set.cc
index d70049421e1ff3472c0017cf51d741271b7a72c3..b0c2cdd8afa0718d133a1ca9d648a19b5cdde211 100644
--- a/chrome/browser/sync/sessions/ordered_commit_set.cc
+++ b/chrome/browser/sync/sessions/ordered_commit_set.cc
@@ -31,6 +31,14 @@ void OrderedCommitSet::AddCommitItem(const int64 metahandle,
   }
 }
 
+void OrderedCommitSet::Clear() {
+  inserted_metahandles_.clear();
+  metahandle_order_.clear();
+  commit_ids_.clear();
+  projections_.clear();
+  types_.clear();
+}
+
 void OrderedCommitSet::AppendReverse(const OrderedCommitSet& other) {
   for (int i = other.Size() - 1; i >= 0; i--) {
     CommitItem item = other.GetCommitItemAt(i);