Implement Invalidator::Acknowledge

sync/internal_api/public/base/invalidation_state.h

Index: sync/internal_api/public/base/invalidation_state.h
diff --git a/sync/internal_api/public/base/invalidation_state.h b/sync/internal_api/public/base/invalidation_state.h
index 8c811afda6684e8ccea314011ce5cb5fb7f46898..b2a57027c355d4ce779e0495b497e8b3989ad955 100644
--- a/sync/internal_api/public/base/invalidation_state.h
+++ b/sync/internal_api/public/base/invalidation_state.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 
 namespace base {
@@ -16,28 +17,34 @@ class Value;
 
 namespace syncer {
 
-// Opaque class that represents an ack handle.
-// TODO(dcheng): This is just a refactoring change, so the class is empty for
-// the moment. It will be filled once we start implementing 'reminders'.
+// Opaque class that represents an ack handle. We don't reuse the Tango ack
+// handles to avoid unnecessary dependencies.
 class AckHandle {
  public:
+  static AckHandle CreateUnique();
+  static AckHandle InvalidAckHandle();
+
   bool Equals(const AckHandle& other) const;
 
   scoped_ptr<base::Value> ToValue() const;
-
   bool ResetFromValue(const base::Value& value);
+
+ private:
+  AckHandle(const std::string& state);
+
+  std::string state_;
 };
 
 struct InvalidationState {
-  std::string payload;
-  AckHandle ack_handle;
+  InvalidationState();
 
   bool Equals(const InvalidationState& other) const;
 
-  // Caller owns the returned DictionaryValue.
   scoped_ptr<base::DictionaryValue> ToValue() const;
-
   bool ResetFromValue(const base::DictionaryValue& value);
+
+  std::string payload;
+  AckHandle ack_handle;
 };
 
 }  // namespace syncer