Refactor NearbySharingServiceImplUnittest for IncomingConnections

- Extract common set up for incoming connections
- Extract common set up for accept / reject flows
- Add a TODO for fetching certificate for outgoing share target based on parent CL

Bug: 1085068
Change-Id: I3b3e322026c3cfe2fe86808f92bfd0b1d810f94b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2344604
Commit-Queue: Himanshu Jaju <himanshujaju@chromium.org>
Reviewed-by: Richard Knoll <knollr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#796503}

chrome/browser/nearby_sharing/nearby_sharing_service_impl.cc

@@ -568,9 +568,10 @@ void NearbySharingServiceImpl::OnOutgoingAdvertisementDecoded(
   // Once get the advertisement, first thing to do is to decrypt its device name
   // based on its visibility and create a ShareTarget to represent this remote
   // device.
-  base::Optional<ShareTarget> share_target =
-      CreateShareTarget(endpoint_id, std::move(advertisement), base::nullopt,
-                        /*is_incoming=*/false);
+  // TODO(nmusgrave): Use valid certificate from certificate manager.
+  base::Optional<ShareTarget> share_target = CreateShareTarget(
+      endpoint_id, std::move(advertisement), /*certificate=*/base::nullopt,
+      /*is_incoming=*/false);
   if (!share_target) {
     NS_LOG(VERBOSE) << __func__
                     << ": Failed to convert advertisement to share target from "