[Sync] Add support for proxy types

sync/syncable/model_type.cc

Index: sync/syncable/model_type.cc
diff --git a/sync/syncable/model_type.cc b/sync/syncable/model_type.cc
index 719f65b89dc816b07dfce59e0a8ed1c0ec27b6a7..7f844308e80fca05ca7298e551d90773c95f13bc 100644
--- a/sync/syncable/model_type.cc
+++ b/sync/syncable/model_type.cc
@@ -27,6 +27,10 @@ namespace syncer {
 
 void AddDefaultFieldValue(ModelType datatype,
                           sync_pb::EntitySpecifics* specifics) {
+  if (VirtualTypes().Has(datatype)) {
+    NOTREACHED() << "Virtual types have no default field.";
+    return;
+  }
   switch (datatype) {
     case BOOKMARKS:
       specifics->mutable_bookmark();
@@ -99,6 +103,8 @@ void AddDefaultFieldValue(ModelType datatype,
 ModelType GetModelTypeFromSpecificsFieldNumber(int field_number) {
   for (int i = FIRST_REAL_MODEL_TYPE; i < MODEL_TYPE_COUNT; ++i) {
     ModelType model_type = ModelTypeFromInt(i);
+    if (VirtualTypes().Has(model_type))
+      continue;
     if (GetSpecificsFieldNumberFromModelType(model_type) == field_number)
       return model_type;
   }
@@ -106,6 +112,10 @@ ModelType GetModelTypeFromSpecificsFieldNumber(int field_number) {
 }
 
 int GetSpecificsFieldNumberFromModelType(ModelType model_type) {
+  if (VirtualTypes().Has(model_type)) {
+    NOTREACHED() << "Virtual types have no field number.";
+    return 0;
+  }
   switch (model_type) {
     case BOOKMARKS:
       return sync_pb::EntitySpecifics::kBookmarkFieldNumber;
@@ -299,6 +309,10 @@ ModelTypeSet EncryptableUserTypes() {
   encryptable_user_types.Remove(HISTORY_DELETE_DIRECTIVES);
   // Synced notifications are not encrypted since the server must see changes.
   encryptable_user_types.Remove(SYNCED_NOTIFICATIONS);
+  // Virtual types have no sync representation and are therefore not encrypted
+  // either. Their underlying implicit types may or may not be encrypted
+  // though.

[tim (not reviewing), 2013/02/05 02:41:58]

'Their underlying implicit types may or may not be encrypted though" is
confusing...  How about, "Note however that a virtual type maps to one or more
real ModelTypes which may or may not be encrypted."

[Nicolas Zea, 2013/02/07 01:18:48]

Done.

+  encryptable_user_types.RemoveAll(VirtualTypes());
   return encryptable_user_types;
 }
 
@@ -314,6 +328,12 @@ ModelTypeSet ControlTypes() {
   return set;
 }
 
+ModelTypeSet VirtualTypes() {
+  ModelTypeSet set;
+  // TODO(zea): add a TABS type here.
+  return set;
+}
+
 bool IsControlType(ModelType model_type) {
   return ControlTypes().Has(model_type);
 }
@@ -482,6 +502,8 @@ ModelTypeSet ModelTypeSetFromValue(const base::ListValue& value) {
 
 // TODO(zea): remove all hardcoded tags in model associators and have them use
 // this instead.
+// NOTE: Virtual types should return empty strings (so that we don't NOTREACHED
+// in tests when we verify they have no root node).
 std::string ModelTypeToRootTag(ModelType type) {
   switch (type) {
     case BOOKMARKS:
@@ -534,7 +556,8 @@ std::string ModelTypeToRootTag(ModelType type) {
 }
 
 // TODO(akalin): Figure out a better way to do these mappings.
-
+// Note: Do not include virtual types in this list. They should never receive
+// or trigger notifications.
 namespace {
 const char kBookmarkNotificationType[] = "BOOKMARK";
 const char kPreferenceNotificationType[] = "PREFERENCE";