sync: Add GetAllSyncData to sync/api

chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc

Index: chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc
diff --git a/chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc b/chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc
index 1dde6a8fb78cb77e4d350e07c2b762b40f180a10..6da1db54821fc80440c48435de4e42bb99deff23 100644
--- a/chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc
+++ b/chrome/browser/prefs/synced_pref_change_registrar_browsertest.cc
@@ -37,6 +37,10 @@ class TestSyncProcessorStub : public syncer::SyncChangeProcessor {
       const syncer::SyncChangeList& change_list) OVERRIDE {
     return syncer::SyncError();
   }
+
+  virtual syncer::SyncDataList GetAllSyncData(syncer::ModelType type) const {
+    return syncer::SyncDataList();
+  }
 };
 
 class SyncedPrefChangeRegistrarTest : public InProcessBrowserTest {