More review feedback

Author: wilhuff

Firestore/core/src/firebase/firestore/local/leveldb_key.h

@@ -132,6 +132,7 @@ class LevelDbMutationKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   std::string user_id_;
   model::BatchId batch_id_;
 };
@@ -199,6 +200,7 @@ class LevelDbDocumentMutationKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   std::string user_id_;
   model::DocumentKey document_key_;
   model::BatchId batch_id_;
@@ -238,6 +240,7 @@ class LevelDbMutationQueueKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   std::string user_id_;
 };
 
@@ -283,7 +286,7 @@ class LevelDbTargetKey {
   }
 
  private:
-  model::TargetId target_id_;
+  model::TargetId target_id_ = 0;
 };
 
 /**
@@ -330,6 +333,7 @@ class LevelDbQueryTargetKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   std::string canonical_id_;
   model::TargetId target_id_;
 };
@@ -377,6 +381,7 @@ class LevelDbTargetDocumentKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   model::TargetId target_id_;
   model::DocumentKey document_key_;
 };
@@ -424,6 +429,7 @@ class LevelDbDocumentTargetKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   model::TargetId target_id_;
   model::DocumentKey document_key_;
 };
@@ -469,6 +475,7 @@ class LevelDbRemoteDocumentKey {
   }
 
  private:
+  // Deliberately uninitialized: will be assigned in Decode
   model::DocumentKey document_key_;
 };