Fix UBSan build error

- Adding missing = 0 to NearbyConnectionsManager abstract methods

Bug: 1087054
Change-Id: Id7386ea9c8a4f3d77cac2111142990e15592deeb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2218054
Commit-Queue: Alex Chau <alexchau@chromium.org>
Commit-Queue: Ryan Hansberry <hansberry@chromium.org>
Auto-Submit: Alex Chau <alexchau@chromium.org>
Reviewed-by: Ryan Hansberry <hansberry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772439}

chrome/browser/nearby_sharing/nearby_connections_manager.h

@@ -105,13 +105,13 @@ class NearbyConnectionsManager {
       PayloadStatusListener* listener) = 0;
 
   // Gets the payload associated with |payload_id| if available.
-  virtual base::Optional<Payload> GetIncomingPayload(int64_t payload_id);
+  virtual base::Optional<Payload> GetIncomingPayload(int64_t payload_id) = 0;
 
   // Cancels a Payload currently in-flight to or from remote endpoints.
   virtual void Cancel(int64_t payload_id, ConnectionsCallback callback) = 0;
 
   // Clears all incoming payloads.
-  virtual void ClearIncomingPayloads();
+  virtual void ClearIncomingPayloads() = 0;
 
   // Gets the raw authentication token for the |endpoint_id|.
   virtual base::Optional<std::vector<uint8_t>> GetRawAuthenticationToken(