[Sync] Services can now always assume processor exists.

components/sync/model/model_type_change_processor.h

Index: components/sync/model/model_type_change_processor.h
diff --git a/components/sync/model/model_type_change_processor.h b/components/sync/model/model_type_change_processor.h
index 5eff158cdba1603f01c9af1b6ec4ba9d1a3f9905..9c9d6be7cd0d381d703ac58921822b010f6bc1ae 100644
--- a/components/sync/model/model_type_change_processor.h
+++ b/components/sync/model/model_type_change_processor.h
@@ -62,6 +62,12 @@ class ModelTypeChangeProcessor : public SyncErrorFactory {
   // Indicates that sync is being disabled permanently for this data type. All
   // metadata should be erased from storage.
   virtual void DisableSync() = 0;
+
+  // Returns a boolean representing if the processor's metadata is currently up

[maxbogue, 2016/10/12 23:40:35]

In general, I find "if <foo>, or not." is better written as "whether <foo>."

[skym, 2016/10/13 19:21:38]

Done.

+  // to date and accurately tracking the model type's data, or not. If false is
+  // returned from this, calls to Put and Delete will not do anything and can be
+  // omitted.
+  virtual bool IsTrackingMetadata() = 0;
 };
 
 }  // namespace syncer