[Sync] Add sync api support for context changes

sync/api/sync_data_unittest.cc

Index: sync/api/sync_data_unittest.cc
diff --git a/sync/api/sync_data_unittest.cc b/sync/api/sync_data_unittest.cc
index 19d88d43053732bbe6789ea057b5449bf56ee5ed..ba82101193e3fa66b25e2e7288ca13c7da1983ae 100644
--- a/sync/api/sync_data_unittest.cc
+++ b/sync/api/sync_data_unittest.cc
@@ -21,6 +21,7 @@ const ModelType kDatatype = syncer::PREFERENCES;
 const string kNonUniqueTitle = "my preference";
 const int64 kId = 439829;
 const base::Time kLastModifiedTime = base::Time();
+const std::string kContext = "context";
 
 typedef testing::Test SyncDataTest;
 
@@ -50,6 +51,16 @@ TEST_F(SyncDataTest, CreateLocalData) {
   EXPECT_TRUE(data.GetSpecifics().has_preference());
 }
 
+TEST_F(SyncDataTest, CreateContext) {
+  SyncData data = SyncData::CreateContext(kDatatype, kContext);
+  EXPECT_TRUE(data.IsValid());
+  EXPECT_EQ(data.GetContext(), kContext);
+
+  data = SyncData::CreateContext(kDatatype, "");
+  EXPECT_TRUE(data.IsValid());
+  EXPECT_EQ(data.GetContext(), "");
+}
+
 TEST_F(SyncDataTest, CreateRemoteData) {
   sync_pb::EntitySpecifics specifics;
   specifics.mutable_preference();