sync: Inject sync/'s dependency on invalidations

sync/internal_api/public/base/invalidation.h

Index: sync/internal_api/public/base/invalidation.h
diff --git a/sync/internal_api/public/base/invalidation.h b/sync/internal_api/public/base/invalidation.h
index cf26112e2244839b056c5fa0906b45cb46afe58d..694ffe73efc4d76e1cd537d5f53b4bb755cbdeac 100644
--- a/sync/internal_api/public/base/invalidation.h
+++ b/sync/internal_api/public/base/invalidation.h
@@ -84,12 +84,10 @@ class SYNC_EXPORT Invalidation {
   // invalidations in order to allow the ack tracker to drop the invalidation,
   // too.
   //
-  // The drop record will be tracked by the specified
-  // DroppedInvalidationTracker.  The caller should hang on to this tracker.  It
-  // will need to use it when it recovers from this drop event, or if it needs
-  // to record another drop event for the same ObjectID.  Refer to the
-  // documentation of DroppedInvalidationTracker for more details.
-  void Drop(DroppedInvalidationTracker* tracker) const;
+  // To indicate recovery from a drop event, the client should call
+  // Acknowledge()
+  // on the most recently dropped inavlidation.
+  void Drop();
 
   scoped_ptr<base::DictionaryValue> ToValue() const;
   std::string ToString() const;