diff -r 000000000000 -r 6474c204b198 mobile/android/base/sync/repositories/HashSetStoreTracker.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/base/sync/repositories/HashSetStoreTracker.java	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,61 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+package org.mozilla.gecko.sync.repositories;
+
+import java.util.HashSet;
+import java.util.Iterator;
+
+import org.mozilla.gecko.sync.repositories.domain.Record;
+
+public class HashSetStoreTracker implements StoreTracker {
+
+  // Guarded by `this`.
+  // Used to store GUIDs that were not locally modified but
+  // have been modified by a call to `store`, and thus
+  // should not be returned by a subsequent fetch.
+  private HashSet<String> guids;
+
+  public HashSetStoreTracker() {
+    guids = new HashSet<String>();
+  }
+
+  @Override
+  public String toString() {
+    return "#<Tracker: " + guids.size() + " guids tracked.>";
+  }
+
+  @Override
+  public synchronized boolean trackRecordForExclusion(String guid) {
+    return (guid != null) && guids.add(guid);
+  }
+
+  @Override
+  public synchronized boolean isTrackedForExclusion(String guid) {
+    return (guid != null) && guids.contains(guid);
+  }
+
+  @Override
+  public synchronized boolean untrackStoredForExclusion(String guid) {
+    return (guid != null) && guids.remove(guid);
+  }
+
+  @Override
+  public RecordFilter getFilter() {
+    if (guids.size() == 0) {
+      return null;
+    }
+    return new RecordFilter() {
+      @Override
+      public boolean excludeRecord(Record r) {
+        return isTrackedForExclusion(r.guid);
+      }
+    };
+  }
+
+  @Override
+  public Iterator<String> recordsTrackedForExclusion() {
+    return this.guids.iterator();
+  }
+}